Too many to name them all, but the first I thought of were:
The most memorable unfunny one was Dennilfloss' thread about the death of Nowheremom. That thread really upset me at the time.
Some of the funnier ones were Preyhunter's threads about the kid with the Halo2 T-shirt, and the first time someone posted the joke about the guy having all kinds of problems in the bathroom at a restaurant and people thought he was serious. Someone tried it again here not too long ago, but too many people knew what was going on for anything to come of it the second time around.
I enjoyed a lot of Russ' threads as well.
Edit: Oh yeah, I liked the Mods Gone Wild thread too.