Whenever I want to get someone to give sci-fi a shot, I always recommend the reimagined Battlestar Galactica. I also love Star Trek TNG, The X-Files, The Outer Limits, Firefly, the earlier episodes of The 4400, & Futurama (do cartoons count?)
But in general, I've always felt that sci-fi on TV always plays second fiddle to sci-fi on film.