Here's a nice rank checker:
http://www.sheerseo.com
Mac Users Note: SheerSeo is an online service, so no Windows software needed. (Also, advancedwebranking.com has a Mac OSX 10.4 version available)
SheerSeo has a 3 month free demo. Looks pretty nice to me. Easy to use, but pretty much data there is you want it.
After demo, you must pay monthly. Plans range from $7 - $15 per month.
SheerSeo is the easiest way to monitor rankings I've seen so far, at least for Mac users. Thumbs up.