I have tried sooooo many of them that I can recommend this one as THE ONE that I have found to be the best.

http://www.tune-up.com

It really works and will not fuckup our PC as a lot of them will do.

The trial is a fully functional version so you can try the entire program out. I am running Vista Ultimate 64 bit version and it works great with that.

Give it a try and you will like it.