Here is my classification of jokes based on mechanism. This is not an exhaustive list, but these are the jokes I have seen and heard the most. There are only about a dozen basic kinds of jokes. Two of the most common patterns are Repetition and Listing. Here are a few of my favorite examples from each:
1. List. A subtype is the medical side effects joke.
2. Repetition. Call-backs are a sub-type here.
4. Sudden Contradiction/Juxtaposition Most sight gags in TV & movies fall here.
5. Pun. Here I include substitution and elimination of words. In other words, just about every porn title ever: Breast Side Story, On Golden Blonde, etc.
6. Shaggy Dog. Usually works better in a visual medium
10. Songs, especially parodies
11. Act-outs. I did an article on these already. Read it now you uncircumcised baboon!
And of course, there are jokes that fit into more than one category:
"Humor can be dissected, as a frog can, but the thing dies in the process and the innards are discouraging to any but the pure scientific mind."
Oh yeah, E B White? Well, if you're so smart, how come you're dead?