Generally agreement with the shout-outs to Babylon 5 and the classics of golden-age sci-fi.
I also recently started the Off Armageddon Reef series. Weber actually has a lot of other stuff that's well worth reading; he's best known for the Honor Harrington books (space opera but with a strang character focus, started out as "Horatio Hornblower in space" but has become very much its own thing) but has written some other excellent sci-fi.
Actually, that's as good a place as any to drop a link: http://baencd.thefifthimperium.com
Baen (sci-fi publisher, in case anybody doesn't recognize the name) puts CDs with freely redistributable ebooks inside many of their hardcover releases. The owner of the linked site takes these CDs and posts the contents online (which is, amazingly enough, perfectly legal - Baen is awesome that way). I won't claim that everything on the site is a must-read, but if you're looking for 100 or so free ebooks of generally high quality, have at it.
Because it must be mentioned, Dragon's Egg. Hard sci-fi about life evolving on a neutron star.
Old Man's War (and sequels) by John Scalzi. Join the military on your 80th birthday, knowing that you'll never be allowed to return to Earth. Quite possibly the best-ever example of taking the basis of Starship Troopers and really running with it, without the heavy political commentary.
The entire Ender's Game series and everything related to it (Orson Scott Card) is another obligatory. I'd also recommend the Homecoming series (Memory of Earth is the first).
Nightfall, both versions.
For sci-fi movies, the Trek movies (to one degree or another) and Star Wars movies (same disclaimer) plus Serenity (of course).
District 9, though it helps that I've been to South Africa and actually have family in the area, which made it easier to associate with the social commentary prior to the major sci-fi awesomeness.
Avatar, it's actually got a lot more science to it than many people realize.
... I clearly don't watch enough movies, because those last two are both recent and I can't recall any others worthy of mention at present.
The Matrix, though I'm less fanatic about it than many.