I'd love to see a new Star Trek series, more than anything. It's been too long since Enterprise was cancelled, and the movies more than prove there is still plenty of life left in the franchise.
The sci-fi genre in general is really lacking on T.V. at the moment. I'd be happy with any decent sci-fi show. I know there's Defiance on right now, but that really hasn't wowed me. And CW's shows aren't really sci-fi at all, they're just teen romance disguised as such.
A reboot of Sliders would be cool to see, too. I loved that show while FOX was still carrying it, it had such a cool sense of exploration and discovery, and had a great cast. After the Sci-Fi Channel took over, though, the show sharply declined in quality and we lost John-Rhys Davies and Jerry O'Connel, the 2 best cast members.
I'd also love to see some GOOD DC Comics cartoons return. Cartoon Network's decision to cancel Green Lantern and Young Justice for the kiddie-version of Teen Titans is unforgivable. If I could have my dream, just make DC Nation a 2-hour block, and bring back Batman: TAS, Batman Beyond, Superman TAS, and Justice League Unlimited with all-new episodes. But that will probably never happen.
Oh, how about bringing back G4/TechTV Icons? Best video game T.V. show, EVER, IMO. Such a cool and entertaining way to learn about the history of the gaming industry. And there were still many subjects and franchises left unexplored by that show.
The return of Headbanger's Ball on MTV would be fantastic, as well. I'm a huge metal-head, and this was the best show on T.V. to see the latest metal videos, see interviews with bands, and the latest going-ons in the topsy-turvy world of metal.