My tests have found RegCure is the best registry cleaner. It found errors other programs didn't, and it wasn't too expensive either (about $30)

But whatever product you choose, definitely get a registry repair program first if you have a slow running computer. No use in going out and spending a ton of money at a repair shop

For 30 bucks I prefer Auslogics BoostSpeed, as it's not only a reg cleaner, but also has lots of other tools, like disk defrag, internet speed optimiser, disk cleaner, history and track eraser etc.

But I totally agree - no need to waste your money in repair shops!