My current gaming group has myself as GM plus eight(!) players. Granted, we almost never have a full table, but we're usually pretty close. It's a ridiculous proposition trying to run combats and keep everyone engaged. But I've finally cracked it:
Turn them on each other!
The half orc keeps failing his will saves against various mind-altering effects and over the course of several combats has ended up trying to kill or injure his companions over and over. I really wish we were recording this game, because it's totally hilarious how he always manages to roll a 1 at the right time.
I used to run 1st Edition AD&D for 8 players, and it was definitely a challenge. But then we had incidents like the Thief being caught taking treasure for himself, and the Paladin deciding that pushing him into a spiked pit would be reasonable punishment. Players wanting to be charmed so they could turn on the party, and the infamous fumble roll where you swung and hit a friend instead of foe. It was chaotic, and a lot of work, but I'd do it again in a heartbeat.