What are some cool "beat the game/challenge" unlocks?

Just saw a mod for Insomniac's Spiderman 2 where you play the game as Venom complete with wings for traversal. This reminded of Raimi's Spiderman 1 game where if you beat the game on hard difficulty, you get to play as Harry Osborn Green Goblin through the main story. He's got a completely different moveset from Spiderman which includes traveling on his glider with machine guns, running in fiery speed, and summoning drones.