This post by Augie de Blieck echoes something I've been thinking about myself for the last few years:

But where’s the science fiction on television now? It’s all gone. The once lucrative syndication market that used to be packed to the gills with sci fi show is now dead. The networks don’t have any shows anymore, and the cable networks don’t want to take the chances.

Part of the problem is that science fiction tends to happen on the margins of TV. The X-Files survived only because it was on the then-fledgling Fox network, which was thrilled at the time to have a well-reviewed show with a dedicated core audience. ST: TNG paved the way for Hercules and Xena in first-run syndication. At WB, Buffy essentially went the X-Files route: It debuted when the network was young and needed press, it was an excellent series, and it reliably brought in viewers who could be drawn to other new shows. Remember how relentlessly Dawson's Creek was promoted during Season 2 of Buffy? It was excruciating for those of us who weren't the typical WB target audience. But today a show like Buffy would probably never make it on the air; WB doesn't need the rabid fan audience the way it did eight years ago, just as Fox didn't need the kind of audience Firefly or Wonderfalls could bring. I'm not sure there are any margins left. Augie notes that Alias is an exception, and he's right, but that's largely because Alias is on a major network that simply doesn't have any new shows and can't afford to lose a show that brings in a reliable audience, even if that audience is smaller than the network would like.