I love the idea of bringing back space shooters, X-wing Vs. Tie Fighter, Wing Commander, Freespace, etc.
In that vein, Star Fox would be another obvious answer, but I feel like that's probably been discussed to death already in past threads. My wish list for that: Make it a true sequel to Star Fox 64, add multiple mission trees, and implement an on-line multiplayer mode for co-op missions or arena battles.
As far as older IPs go...I really, really would have liked to see Capcom make a Mega Man Legends 3. As clunky and silly as that series was, it had a lot of charm. I loved the Saturday morning anime-type feel to it at the time.
I'd love to see Ubisoft give another try for Beyond Good And Evil 2, but I'm losing hope that the series will ever again see the light of day.
Also, for really old games, I'd love to see a remake of Faxanadu, Clash At Demonhead, or the Magic of Scheherazade. Clash at Demonhead, in particular, was so bizarre, that I'd love to see what someone like Wayforward could do if they had the rights to it.
Blaster Master would have been on that list as well, but they did release a sequel of sorts on Wii Ware earlier this year. I wouldn't mind seeing them give it another try, with some changes to the game mechanics. Otherwise, I loved it.