Karma is a good top laner that you don't often see. She can bully the crap out of melees in lane, and is extremely hard to gank. She's super strong in the early and mid game. Her damage scales down a bit in the late game, but she has amazing peel for her ADC, and ends up filling a sort of poke/off-support role.
GP is known for being a top laner, but he's not popular at all right now. GP is one of my favorite champions to play. I carried myself to plat maining him in ranked. He's criminally underrated right now in my opinion. If you're interested, I'd be happy to give you advice on building/playing him up top.
Swain is starting to catch on in the top lane, but you can still surprise people with this. He's a massive lane bully who beats pretty much every melee in the game post-6.
Volibear isn't in a great spot, balance wise, but he's still a super fun (if horribly predictable) top laner. Don't pick him though, unless you know you are going against a melee who wont be able to kite you. Volibear lanes horribly against ranged champions, since he has no reliable sustain, no wave clear, and is easy to kite.