I've been using this for a while and think it's worth recommending.
Basically, regprot monitors your registry and will not allow a change till you are prompted to allow/refuse.
Humorously, it even prompts you when you install it.
Since so much malware likes to infect the registry (and can be a bitch to find/remove) I think this is a worthwhile addition to anyone's security suite.
It's small (148k), free and effective...what more could you ask for?