I believe anaglyph is for viewing with 3D glasses. Perhaps stereo rendering is for cross-eyed people?
Stereoscopic rendering refers to any technique which creates an illusion of depth by rendering two separate images. Anaglyph is just one type of stereoscopic rendering. Yes, anaglyph images are viewed with old-school red/blue 3D glasses.
Other types of stereoscopic rendering include the "cross-eyed" technique, which you mentioned, and page-flipping, which requires shutter glasses. I don't mind the cross-eyed technique that much, but it does give you a slight headache after a while. Also, some people have a very hard time getting their eyes to focus while crossed.
I used to have a pair of shutter glasses which worked pretty well. The 3D effect was incredible on some games (Dungeon Siege, Descent). The downside is that you lose some of the "smoothness" of the animation, since the left/right images are rendered in sequence rather than at the same time. So on a 90 Hz monitor you're really only getting 45 FPS. Also, games which integrate 3D and 2D effects would break the illusion of depth. Specifically, 2D smoke and fire sprites look more unrealistic (and Tremulous uses both).
Unfortunately, my shutter glasses stopped working when I switched to a computer with an ATI video card. The stereo drivers couldn't handle OpenGL games on my video card for some reason.
EDIT: If you're interested in trying out shutter glasses, I got mine from e-Dimensional. However, your monitor must use a VGA connector (not DVI), and I wouldn't risk it with an ATI video card. I'd also investigate the specific games you're interested in to make sure they're supported.
