You could also take a look at the Yeti3D engine, which is somewhat faster than Quake, iirc, though perhaps a little less versatile. It hasn't really been used as yet, though I believe it is at the heart of the (now renamed) Medal of Honour GP that a team is working on. There is a demo that comes with it that you could try out, but I don't know where to get it from.
There's also a .md2 or .mdf2 (can't remember which) dancing demon demo put out by Thor (rtb7) a while back in the Beta testers section. However, I do not believe he is working on it anymore; I could be wrong though. I read somewhere that he had quit the scene some time back due to people claiming that the brilliant KoF 91 wasn't any good and slating him for it; on the other hand he recently posted in the GPChess thread, so who knows. Thor, feel free to give me a slap if I'm wrong. Indeed, I'd be grateful if you would lol!
You could also take a glance at GoatPark32 which has some very very nice Voxel rendering in it from over a year back well before most 3D stuff had been remotely done (barring Doom, which many claim doesn't count on account of not being "true" 3D). In addition, there's a 1-track "racing" (or at least, driving) demo put out by the same author - Mithris - a while back, which demonstrates some more nice 3D stuff. And not to forget "15 day crap" from the first 15 day competition. Which is untextured, but fast and very playable.
Other than that? I believe there have been a few games released on GP32spain recently which are done in pseudo3D (a sports game and a Tron-like one), but I haven't actually tried them.
Or of course, there's a GBA 3D demo which you could run on GPAdvance at easily full speed. If you get hold of a very very early version, in fact, you'll find it runs at 10x the speed of its rate on GBA hardware. Which is impressive perhaps.
Beyond those, I can't think of any. If I come up with any I'll post again. Most impressive are Quake, Yeti3D, and GoatPark32, imo, though.
