Seobook has released a very nice firefox extension call Rank Checker. This is a free open-source tool that will show your rank for specific keywords on Google, Yahoo, and MSN.

Using a rank checking tool is a real time saver. Rather than try to dig through results to find your site, this will give you the data in just a few seconds. The best way would be to export the data each time and name each file with the date it was run. This way you can track your ranking changes over time.