Now these are not the newest tools on the internet but I have just been working with them and have found the information invaluable in building good search ideas.
The first one is of course from the one company who has blazed new trends in internet searches, you guessed it Google. If you have not created an account in their webmaster center I highly recommend you do. The nice part of this tool is that you will get feedback on what terms people are using to find your website. It used to be a stab in the dark but with their tool set you get a better idea of how Google has been searching your website.
One tool that I have started to keep an eye on is the "top search queries". In here they tell you many nice tidbits of information like where you place in that search term and you can also verify that by clicking on the term. Also on that page is statistics of your click through rate which help you understand how people are finding your site.
The next great tool they have is keywords that Google has found on your website. Make sure to watch this list because it can help you add more words to your meta information.
Now there is a lot of information in this tool so I will let you create your own account and explore the many different stats Google provides about your website. The one tool though I want to point out is their diagnostic tools. If you have ever wonder why Google may have skipped reading a page this tool will tell you. Under diagnostics there is the HTML Suggestions tool that will give you feedback on what you need to change to help your search engine friendliness.
Google isn't the only search engine that has these tools. Make sure to check out Bing and see their tools. You can tell there is a difference in layout and information but they both give you tips on how to improve your friendliness to the web crawlers.