Pokemon Ash Gray
This has got to be one of the funnest hacks of Fire Red that I have played. It follows the story of Ash in the anime but in game form. It does a really good job at it too, what with Pikachu not liking Ash at the start, and stealing the bike from Misty to rush to the Pokemon Center. Very cool way of hacking a game, and it's a lot of fun and well worth your time.