Everyone's hitting on my faves
StarTrek: TOS, Voyager, Enterprise (not so much TNG or DS-9, a little to lib preachy)
StarGate SG-1 (not so much spin-offs)
Ark (Haven't seen in long time)
Silent Running (haven't heard anyone mention that in decades)
Good stuff from your side of the pond:
P.K. Dick, Asimov, Poul Anderson, R. A. Heinlein (the terribull spellur), Arthur C. Clarke (the indisputable king of hard science), Harry Harrison, Ben Bova, E.R. Burroughs... so many I've forgotten about over the years... definitely Orson Scott Card (he's a master at character development). Larry Niven and Jerry Pournelle (both his books and his "Computing at Chaos Manor" columns for Byte magazine back in the day). Even Stephen King, he says he's terrible at Sci-Fi, but I remember a couple of short stories he'd written in that were quite good, plus Dark Tower series incorporates some SF elements brilliantly, he underestimates himself.
Recently, I got hooked on H. Beam Piper, Pournelle was his editor at Tor back in the early '60's before he committed suicide. Such a loss. Great writer, great social analysis. Had he lived, he would have been intrigued by, and probably predicted a lot of political trends and current events, esp. in Middle East. I would love to see his stories get a tech update and brought to the screen.You'll find some of his stuff at Project Gutenberg at http://www.gutenberg.org/