Half Life Ok, now that the troll quota has been met...
How about another 3D Bomberman game? If Sonic can get another chance after Sonic 06, Bomberman should get another chance after Act Zero. There have been good 3D Bomberman games, so that's good, at least.
Skies of Arcadia 2. You have a massive, unique world with all sorts of history to it, great mechanics, and unique gameplay. This game NEEDS a sequel.
Alpha Protocol 2. The original wasn't that good. But the concept has potential. So maybe given another chance, it could shine. Or it could just suck and we can move on.
Star Wars Battlefront 3. With the rise of online gaming, the public's love of TPS and FPS games, and considering how LucasArts loves milking the Star Wars cashcow, how this game HASN'T been made is one of the biggest mysteries in the history of gaming.
Diddy Kong Racing 2. Honestly, this game probably shouldn't be made considering the recent track record of Rare. So if Rare gets their act together, this would be a great way to show the gaming public "Hey! We're back!"
Marvel Ultimate Alliance 3. What can I say, I'm a comic nerd... just make it more like the first one, but keep some of the improvements from 2.