I recommended to a friend that he installs a registry cleaner (I have used CleanMyPC quite happily for a long time), so I searched and found several review sites e.g. registrycleanerguide.org, registrycleaners.com. Looking at them I find them suspicious. They all differ in their results, of course, but I get the feeling that they are set up by the sellers as a front to their products. I notice that none of them quote a price (only "free" download) and even the individual company sites refuse to display a cost until you enter your name and email address. I am reluctant to download something that will go fiddling in my registry. Am I just a bit too suspicious? Perhaps it is just commercial tactics.

The only one I ever use is CCleaner as that has a registry cleaning part - and it's free! http://download.cnet.com/ccleaner/

+1

I may have used this one in the past too http://majorgeeks.com/Microsoft_RegClean_d458.html

+1 for CCleaner.

Thanks for these - I agree about CC and have recommended it.
One thing it doesn't seem to do that CleanMyPC does, is look for File/Path references to non-existent files. It currently finds about 250 such broken links. Some will be system files that are not setup etc. so I am careful which ones I delete.