Slaughterhouse Five is plenty fucking weird! It starts out as a person talking about the war and just randomly develops into a....I think the word "clusterfumble" is appropriate here. I'm sure there's some really obvious point its making, but I can't for the life of me figure out what it is.
One of my favourite books is called The Raw Sharks Texts* by Steven Hall. Absolutely brilliant, but absolutely completely batshit crazy. About a bloke from Derby (England, he's an English author) being chased by the concept of a fish. Yes, its as ridiculous as it sounds, but is one of the most brilliantly inventive novels I've ever read. I've read it three times now and I still can't figure out the ending. Highly recommended.
The Book Thief by Marcus Zusak is pretty weird as well, mainly because its narrated by death. Very very good though.
Thing is, I like books to be a little weird, but if a book is weird it needs to be especially good, because you aren't going to put up with that sort of thing from an average book are you?
I've never read it, but isn't it the Life and Times of Tristam Shandy that is a man's autobiography where he never manages to get beyond his own birth? That sounds weird!
*You see, its a pun on Rorschach tests.