If you’re just starting in SEO and trying to learn as much as you can about Search Engine Optimization, your budget is probably going to be very limited (or perhaps even non-existent) but that doesn’t mean that you can’t gain access to some of the most useful SEO tools around.

Sure, there are more advanced tools out there if you’re willing and able to pay for them or, better still, if you have the resources and skills to create custom tools for yourself, but if you’re just starting out these free tools will give you more than enough information to help build your skills and understanding of important SEO-metrics.

If you end up doing so well that you can afford to shell out for better tools, that’s great.  If you can afford to get your own custom tools developed, that’s even better.  But you won’t notice the real benefits of expensive solutions like that until you’ve learned the basics from using free SEO tools like these.

So, what are you waiting for?
Check out this list of great SEO tools and go get ‘em!

1. Firefox- The web-browsers’ web-browser.  No SEO should be without it.  Firefox is free, flexible and can be extended by adding the plugins mentioned below in order to become an incredibly powerful tool for gathering SEO information. 
   I’ll admit, I tend to use IE for my day to day surfing (simply out of habit as I’ve been using it for years and I’m used to it’s particular quirks - I also feel that it’s a good idea to use it because it’s the default browser for so many people out there, which means it’s worth seeing sites the way everyone else does).  Don’t be a browser snob just because Firefox does so much more for you and does it better - Use FF when you need the SEO tools and other useful tidbits, but spend some time surfing with IE as well; most users aren’t as savvy as you are, try to see the world wide web from their perspective, at least for a little while.
2. SEObook’s Free Tools- Aaron Wall has created and made available some fantastic free SEO tools and he always provides really clear and helpful write ups on how to install them and get the most out of using the tools - my particular favorites are the SEO for Firefox plugin and the recently released Rank Checker tool which allows you to check a website’s rank in the big 3 search engines for your chosen keywords and provides a myriad of options to tailor it to your own needs and regional search engine preferences.
3. Joost DeValk’s SEO Tools- Joost makes some great plugins for WordPress and some brilliant SEO tools for Firefox as well.  Personal favorite here is his link analyzer, which will add information about pagerank, anchor text and rel=nofollow status for links to your site in analytics packages like Google Analytics or Yahoo Site Explorer.  Very useful indeed.
4. Keyword Research Tools
   - SEObook- Throwing some more link love Aaron’s way, the SEObook keyword tool will run checks across a variety of search engines for you and present you with a table full of results with loads of information that as a beginner you probably didn’t even realise was important.  Drink it all in, getting your head around this sort of detailed information about your targetted keywords is what it’s all about.
   - Google Keyword Tool- The data you’ll get from Google’s own tool isn’t quite as expansive as you’d find with some of the others and is focussed more towards use when setting up PPC AdWords campaigns, but it can be helpful when you’re in need of some quick comparisons of relative search volumes or if you want to get an idea of how competitive a particular keyword may be, based on the amount of advertising competition shown.
   - Wordtracker’s Free Tool- Wordtracker don’t give a lot away with their free tool, because they’d prefer you to pay for access to their excellent full tool, which can be bought fairly cheaply for very short-term access.  In fact Wordtracker’s full tool is one of the few premium tools out there that I would suggest paying for during the early stages of practicing SEO, but only for those occasions when you really need it.
5. Google Toolbar- If you haven’t installed this for both of your web-browsers (you are using IE and Firefox now, aren’t you?) go and get it now.  If you want to be really thorough you can also add toolbars from Yahoo! and MS Live Search, but you could end up suffering from toolbar overload and covering up most of the visible area of your browser window.  I tend to just keep the other two toolbars switched off and only turn them on if I really need to check something for that particular search engine.
6. Search Engines’ Webmaster Tools and Analytics Packages
   I’ve heard a few more experienced SEOs suggest that you should stay as far away as possible from search engines’ own analytics packages on the basis that you don’t want to be sharing all that sensitive information with “the enemy.”  Perhaps it’s because I’m new at this, or because I’m determined to try and keep my hat as white as possible, but I fail to see the logic of that argument.  If Google and the other search engines want to give me an easy way to see how well they’re indexing my site and make sure that they can find my sitemap, why shouldn’t I use it?  Granted, none of these options could be described as a complete solution in and of itself, but surely it’s better to have this information and not need it than to need this information and not have it?
   - Google Webmaster Tools - Lets you “suggest” various preferences to the Big G in terms of things like crawl rates, preferred domains and geographical targets but features their typically fuzzy worded statements about how effective this may be; in other words Google will still make up their own mind about how to treat your site, regardless of what you ask them to do.  Data presented about incoming links from external sites can be useful, but always tends to lag a few days (or even weeks) behind the real world and doesn’t give a full count even when it does update.  Will also let you see some (but not all) of the search queries for which your site has appeared in the SERPs and which ones resulted in clicks through to your site.
   - Yahoo! Site Explorer - A much better way of checking links to your site, especially if you’re using Firefox with Joost’s Link Analysis plugin; this will enable you to see whether the incoming links are passing pagerank (and the PR of the linking page) as well as the anchor text used on the page.  Very useful to know.
   - MS Live Search Webmaster Centre - They don’t give a lot of information away here; just ten inbound and outbound links, which they say are “performing the best” but it’s unclear how they rate that performance and they seem to just pick the links at random.  Live search can take a good while longer to fully index your site than the other engines.  Give them a helping hand by pointing them in the direction of your sitemap, then drop by occasionally to check how many of your pages have been indexed.
   - Google Analytics - This one is really useful when you’re building up your site and starting to get traffic coming through.  Enables you to see a whole load of information about your visitors, from referring sites, depth of visit, geographical locations, browser types and more.  Much easier than trying to divine this sort of knowledge from your server logs and a great way to gain a better understanding of how well your site’s being recieved.  Doubtless there are better ways to analyze your site’s statistics, but until you can afford to pay for them, this is top dog.
   - WP-Stats- Recently added to the ever-growing list of must-have WordPress plugins, WP-Stats is Automatic’s (the company behind WordPress) own way of getting statistics about your blog’s performance.  It’s far from the most detailed information in the world, but it highlights the important things like number of visits, their sources, even search terms that brought people to your blog and it puts it all into an easy to understand format on your WordPress Admin Dashboard.  Great for at-a-glance updates before you go digging into Google Analytics for more details.
7. SEOmoz’s SEO Tools - Rand Fishkin and the gang over at SEOmoz have put together a really handy collection of toys.  To get the full benefit you’ll need to sign up for their Pro-membership package, but there’s still plenty of things you can do with their free tools.  The Page Strength tool is great for getting a quick overview of a wide variety of ranking factors for your chosen URL and although the free tools have a daily limit on the number of times you can use them before you have to sign up for a premium account, I would recommend trying out the various tools on offer so that you can build up your understanding of the sort of factors that you need to consider when optimizing a site for search engine rankings.
8. Bruce Clay’s Free Trial SEO ToolSet - Much like the SEOmoz tools, Bruce Clay’s SEO ToolSet is primarily designed to be used as a premium, paid-for, product by more experienced SEOs but they also allow for a limited, free-trial access.  The tools available here can provide you with a wealth of information, but in my opinion you’d be better off waiting until you’ve gained a greater understanding of SEO-metrics from some of the simpler, more easily accessible SEO tools out there before delving into more advanced tools like these.

I’m sure there are plenty of other free SEO Tools out there that I’ve neglected to mention, these just happen to be a few of my personal favourites and are the ones that I use most regularly.  Also, this post was getting dangerously close to turning into a top 10 list and you know I’m not a fan of them.

If there are any tools that you think I’ve missed and that would be useful for people just starting to learn about SEO then feel free to comment with a link to your recommendations.  If I get enough (any) good suggestions, I’ll update this post to include them and give credit to the person who pointed it out.

 Update (before I actually post):  Before I finished this post and published it I decided to ask the Twitterverse if they had any recommendations for useful, free SEO Tools and got a response within a couple of minutes.
So, props to @BarryBowman of Search Engine News for reminding me about Google’s Website Optimizer.  As Barry says,

I highly recommend Google Optimizer for conducting A/B and Multivariate testing. 1% to 2% can be a dramatic increase to your bottom line!

@SpostareDuro was quick off the mark as well, with links for Alexa.com which can be useful for comparing your site’s rating against your competitors and other, similar sites.
I also want to point out her post about Keyword Research Tools.  She links to a few extra tools that I’ve missed off my list and explains in a bit more detail about what some of these tools can help you find out.

 Update 2:  Bill Slawski from SEO By The Sea dropped by and recommended a really useful tool for checking links.  It’s called Xenu Link Sleuth and it’s great for checking your site’s internal linking structure and outbound links to make sure you don’t have any broken links that search engines may frown upon when spidering your site.  Very handy for performing regular health-checks on your site, especially as it grows and find yourself with a large number of pages and links to look after.
Thanks for the tip Bill.