For search engine positioning you can't go past DigitalPoint's keyword tracker.

It allows you to track keywords for more sites than just your own so you can track your performance against a competitors. I track my clients - and since some are competing for the same keywords it can be quite interesting - on one set of keywords I've got 2,3,4,6,7 & 9 - pretty good!

I've attached an example of their graphs.

Sarah