Aaron Wall has written a pretty awesome rank checker tool Firefox plugin that checks various keywords against results on Google, Yahoo, and Microsoft Live. Here's a sample screenshot of what you're expected to see:
While it looks like it's pretty accurate from my perspective, on Sphinn, one of the users note that it isn't completely accurate. Aaron has responded to inform us that the tool "clusters 100 results per page to minimize scraping on Google. That clustering can cause a shift in ranking compared to only seeing 10 results per SERP."
But I gotta say -- this is probably one of the tools that should have been made earlier and just hasn't been. Now, you really don't need an API key to run ranking tools. You can do it out of the convenience of your web browser. Thanks, Aaron. This rocks.
Forum discussion continues at Sphinn.