Reflective water might be easy to draw because water surface is rarely oblique unless you want very big waves. And reflective water is mainly what I'm looking for.

I've been trying to come up with ways to render reflected terrain without using a stencil buffer, and I haven't been able to figure out anything that would actually work. A user clip plane (as Q3A uses) would be helpful, and z-buffer tricks can be used to an extent...

Hmm, perhaps if the water's surface was made into a user clip plane for _both_ the rendering of the reflection and the rendering of the terrain. Then the edges should meet perfectly at the water's edge, and a semi-transparent water surface could still be rendered over. You would lose the visibility of the lake/river's bottom, but would gain terrain reflections... Right now in TM you can see the bottom of the water area, and the surface reflection is just the environment mapped sky. Using a user clip-plane while OpenGL rendering all terrain geometry might be slow on some (if not all) consumer hardware though.