the one i downloaded is called regscrub and it seems to be a pretty good program. of course you want to make sure to do thorough backups first, yadda yadda ;-)
by no means exhausive list, but here's some program lists:
http://www.answersthatwork.com/Taskl...s/tasklist.htm
i think reinstalling windows every once in a while is a good idea, although it is much easier if you have an easy way to backup - ideally a second hard drive