I've used this software before:

http://www.spectorsoft.com/keylogger.asp?refer=27032


I liked it...you can hide it from the process tree and make it so the only way to pull it up is to hit a series of randome keys (I.e...SHIFT + ALT + CTRL + F10) etc....

Not only does it keylog, but it will take a screen shot at a user specified interval, record IM conversations, websites, etc etc...its pretty powerful.

Thats the only one I have experience with.