Farmer 1.....
Before you do, take a look at (free)
RegSeeker 1.45. ...It's very thorough, so make sure you enable the backup first, although unwise not to with any of these programs. ...I've been using it for about a year.
I'm not sure about the availability of the Microsoft equivalent now on the web, but I know it is no longer supported by them and am pretty certain I have read recently that it shouldn't be used with their latest OS's.
Reg
Cleaner mentioned in a previous post is quite old now, no longer being updated since the concentration on the paid version. ...That said I use it, not for registry cleaning, but for it's very useful opening page that allows you to see and deal with what is actually registered to the registry (quite a few surprises here).
I agree CCleaner is absolutely fantastic for what it is designed for, but registry cleaning is a secondary function. ...If anyone is in any doubt, do one on this program and then do one with RegSeeker mentioned at the start.