Like defragging, XP does a pretty good job of keeping the registry neat. I said neat, not clean. But for those of us (me included) that just like to see some of those old entries removed, I use CCleaner and RegScrubXP. And RegScrubXP has some really neat tweaks and utilities.
Can anybody suggest a reliable and good registry cleaner service? I will be greatful if you already had experienced using it and sharing here...

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic