On note, some recent ideas for hacks:
1. (GB/GBC/SGB) Tyrian 2000 Endless - Basically add a Save Prompt after the Credits Screen to allow the player to play from the first level but with all upgrades you had in the last level.
2. (NES) Silver Surfer Health Bar - Remember that shitty game for NES? Why not take AVGN's advice and add a health bar to it?
3. (PC) Tyrian 2000 Extra - Just add secret ships (Like NortShip Z, Dragon, U-Ship) as purchaseable before Ziglon's Revenge and make it so you don't always get Foodship Nine (Yes, I always get Foodship Nine after Episode 5).
4. (PC) Dragon Ball Zandronum: Deathmatch - Do you remember of some Dragon Ball Z mods for Quake and Unreal? Yeah, that kind of mod, but for Zandronum (An online Doom source port with MANY new commands to toy with). It would be pretty neat!
5. (???) Dodonpachi GB - Okay, this cannot be done from any base, so it would need to be a "new project". Basically demaking Dodonpachi as if it was released on Game Boy Color, but (if made on Game Maker or any PC program) taking a few liberties from the limitations GBC would have.
6. (Many) Legend of Touhou - No set name. Just a basic idea to reskin or hack various Zelda games to have Touhou characters, scenery and maybe challenge (bullets everywhere, but no 1HPW). Could be done in Armageddon Games's Zelda Classic.