If you go to
www.fstdt.com, you'll find a site called Fundies Say the Darndest Things and its two sister projects, Conspiracy Theorists Say the Darndest Things and Racists Say the Darndest Things. The racists page is sad rather than funny and the "fundies" page varies (although they are fair enough to include nutballs of all religions, if they find quotes in English) but the conspiracy theorists page is usually laugh-out-loud funny.
For astronomical conspiracy theories, you can check out Phil Plait's "Bad Astronomy" website at
www.badastronomy.com. He debunks a number of things, like the "moon landing was a hoax" theory and the "face on Mars" notion, and he's pretty readable while doing it. (For example, as part of his face on Mars debunking, he includes an amusing essay and a photo of when Lenin's face appeared on his shower curtain—or, rather, he demonstrated how people connect dots and blotches into faces, more or less instinctively.)
There's also a forum connected to badastronomy, and every once in a while someone will drop by and try to push their conspiracy theories. Since Phil Plait and some of the regular posters are professional astronomers, they usually get their rearmost parts handed to them.
I think James Randi has a similar site, but I haven't really gone exploring it. You might be able to get an interesting notion or two off of snopes, though, just by taking one of their debunked legends and inventing a cover-up around it.
Izunya