Pookthetook actually wrote a plugin that interfaces with the CleverBot API in which when people would message you in-game, it would reply using CleverBot's responses.
I don't believe he had published it publically, but it would most-likely need some filtering and tweaks before it would be worthy of a public release given that there's some things that would need to be handled with actual WoW-related text.
Aside from that, I'm not too sure of any.