Here's a few basic ones that nobody seems to have mentioned yet:
Tiling option for diffuse textures (what we in SL know as textures right now) with UV mapping outside the normal space. Default would be 'Repeat' (normal SL behavior), with 'Extend' (extends edge color past boundaries) and 'Flip' (mirrors texture past boundaries), possibly with separate Horizontal and Vertical options.
'Sprite' option. This would need documented, but would cause the geometry facing a certain direction (say, positive X, like avatar meshes) to render similar to a static, unfading particle. Unlike a particle, th