Infinity Suicide v4.0
Five levels, some ported from M2 suicides, some brand new. All quite playable (except maybe Kevorkian's Rooms, which will give you a horrible headache). Deadly Ledges is very nice for extremely high-carnage games.
Levels in map "M∞-Suicide4":
Basket Hangin' MotherFucker
Deadly Ledges
Pistol Parlor2
Kevorkian's Rooms
Otis' Place