1. stating the obvious 2. sarcasm and 3. someone slipping on a banana peel and falling.
I see another thing in some stand-up comedy - namely, profuse profanity. Somehow that is considered funny.
1 and 2 I would agree with. Humour is very subjective though and I don't find the "slipping on a banana" type of slapstick comedy funny at all.
As far as lots of profanity (swearing/cursing) is concerned, I'm sure that many people would automatically find that not funny. I'm not one of them but it entirely depends on the stand-up comedian. There are a couple of current comedians who do that and I think they're hilarious. Billy Connolly's 1970s and 1980s stand-up shows contained the word f*ck more times than you could possibly count but they were incidental to the very funny stories he told. However, in a way that I really can't explain, the swearing did actually add to it.