Well you've started with what I consider pretty much the pinnacle of Sci Fi, with Battlestar Galactica taking my vote for best Sci-Fi series of pretty much all time.
My second choice, however, would be the Stargate series. The series was based off the Roland Emmerich movie, which basically serves as a pilot. You don't need to watch it first or anything (I didn't). The plot revolves around the discovery of a device called (funnily enough) the Stargate that allows instantaneous transportation from one planet to another, allowing for exploration of the galaxy.
Stargate SG-1 (the main series) is a great sci-fi romp, very funny with witty writing and great stories. It is 10 seasons long, however, (making it the longest running sci-fi TV series in American history) meaning that if you get into it you've got a hell of a lot to keep watching, but you can't begrudge the series its success. If you're looking for more sci-fi, Stargate SG-1 is one of the best out there.