I recently came across a very useful tool for SEO. Primarily, NicheBot (http://www.nichebot.com) is a keyword identification tool that uses the WordTracker system on the back end. It's very simple: you enter a search phrase and it will display some information about the volume of searches for that phrase and for a number of other phrases. If you search for a two word phrase, NicheBot will also display 3 and 4 word phrases that contain those words. And by clicking on each of those phrases, you can drill down even further. This can be a great (and quick) way to research keywords for both pay-per-click and SEO.
NicheBot also has a Google rank checker tool that is just as quick and easy to use. Just enter a list of keyword phrases, enter the domain you want to check, choose the number of search results to check, and you are done. And you can even bookmark the results for future checking.
Finally, the NicheBot toolbar makes it easy to do both of the above from any web page, and includes the ability to highlight a phrase on any web page, then right-click to use NicheBot to do some immediate keyword research on that phrase.
I use other tools for large scale keyword research and rank checking, I have been using NicheBot the past few weeks for doing quick rank checking and premilinary keyword research, and it works great.