Sounds for themes

I have quite a few themes but not too many various sounds. I have gotten a few from microsoft.com but it's hard to find what you want using "search". You get obscure or no results. They're also difficult to use, as they're saved in your Media Clip File. Does anyone know where I might find good sounds to accompany the themes? By good I mean better than just stupid "laugh" or "boom" .wavs. Something that really sounds like a sound suite.