The ending to Mighty Max. Apparently the writers didn't want to write a REAL ending, so they did the "time warp to the beginning of the series" thing.
The ending to Trigun gets on my nerves, too. It seems like they couldn't think of a way to resolve the issues between Vash and Knives, so they just had Vash kick Knives' ass. (It was a good fight, though)