There are a bunch out there. If you would like one to view SERP's instantly I find Rank checker (the SEO book firefox plugin) handy. If you would like the keyword service to monitor the progress over time the best oout there Authority Labs (It has some of the best export and filter features available). SEOMoz also has a handy keyword tool: Keyword Tracker.

However, there are two things to keep in mind when using a SERP service: 1. Don't obsess over the position or rank of a keyword every week. Keep in mind that search engine rankings fluctuate often and the natural variation of a metric within control limits always takes place. At the same time, you should know when the keywords is losing rank consistently or when it has gained rank significantly due to your efforts.

2. Always ties in gains and losses shown by the keyword tool with your Analytics. Asking questions like I have improved my rank from 30 to 3 over this keyword, has it brought me improved traffic and most importantly has the traffic converted. This will help you distill out keywords over time to help you focus your efforts.