I may be a little late to the game, but as a television junkie, I think it's my duty to make a few recommendations. Battlestar Galactica would be near the top of this list, but it looks as though you're already enjoying it, which is fantastic. Personally, I'm going through withdrawal (the series finale recently aired).
Buffy the Vampire Slayer
My personal favourite. It works on just about every level. It's great if you just want to be entertained, but it has enough meat to it, that you can watch it for academic/intellectual purposes, as well. Personally, I'm not a huge fan of the first season and a half of the series. They're mostly solid episodes, but I don't think they really represent what the series is. I'd say the series defines itself around episode 13 of the second season.
Friday Night Lights
I had no idea that this show would be so very good. I'm not a fan of football, but it's fascinating to see how much passion the characters in this show have for the sport. It quite honestly defines their life. This is a very realistic, almost voyeuristic show and I'd say it's probably the best thing on television right now.
The West Wing
Unfortunately, this show was only able to keep its quality up for the first four of its seven seasons. But those four seasons are fantastic television. Much like Battlestar Galactica, there is a very cinematic quality to this series, accomplished by stellar writing, directing, and acting.
Six Feet Under
This is a show that I didn't realize would be so emotionally involving. Be prepared to be addicted to it - once I started, I quite literally couldn't stop. I finished the entire series (five, 12-episode seasons) in under one week.
Firefly
This is a series that was cancelled about eight seasons early. I wouldn't necessarily describe it as science fiction (it's more of a western drama), but it is set in space. In fact, the special effects were done by the same people who went on to do Battlestar Galactica, so you'll notice the same aesthetic. Though you will almost certainly be devastated, when you realize there are no more episodes beyond the 13th, there is a feature film continuation called Serenity.
Veronica Mars
This is a really well-written, fun series that I highly recommend. The first two seasons have their own season-long mysteries that are very, very engaging and Kristen Bell is fantastic as the title character.
Strangers With Candy
A wonderful, highly offensive piece of comedy starring Amy Sedaris, Paul Dinello, and Stephen Colbert. I'm not even sure how to describe it.
Shows that I'm currently watching on televison (some are on break):
Dollhouse
30 Rock
House, M.D.
Chuck
Friday Night Lights
Dexter
United States of Tara
Weeds
Family Guy