HijackThis : A general homepage hijackers detector and remover. Initially based on the article Hijacked!, but expanded with almost a dozen other checks against hijacker tricks. It is continually updated to detect and remove new hijacks. It does not target specific programs/URLs, just the methods used by hijackers to force you onto their sites.
As a result, false positives are imminent and unless you are sure what you're doing, you should always consult with knowledgable folks (e.g. the forums) before deleting anything. There are many cool tools here, browse around!