Qbasicnews.com

There's a language called FORTH that can recompile itself, boot from a disk, is a full-fleged OS, etc...

You can redefine almost the whole language, AFAIK.

I saw a wierd language at www.thefreecountry.com in which the entire vocabulary was swear words.

Brainf*ck is pretty weird.

Try prolog, nothing like it.
Haskell is also a cool language once you know it.