None. I've only had one, and that was the clan lag mod. It reduced the lag when you were in a big clan (without it was nearly unplayable, but its not needed anymore).
Some mods are stupid. I hope S2 bans them. Allowed mods should be necessary mods like the clan lag mod, or for fun modes only like the party zephyr mod. Using mods that improve your performance ingame like Last Hit Assists, is cheating imo. If you suck that much why dont you just install a bot to play for you? Please, never use any stupid mod like Last Hit Assist, it wont make you any better at the game but still give you an advantage over other players. Unfair.
/endrage