Ray Tracing

Goddamn all of these homework threads. Let's talk about something interesting.

I'm starting work on a ray-tracer for shits, /proggles/ Any tips on speed improvements? It's being written in C.
I know the show stopper (usually) is having to check each element in the scene and see if it has been intersected by a casted ray. Any ideas on improvements in that area?

In short ray tracers:
1.are inefficient by design vs OpenGL effects(which are more complex and provide flexibility in design)
2.use horrible,uncached computation architecture which has zero environment knowledge(rays to pixels blindly shot everywhere)
3.typically have a huge inner loop with multiple branches. Branches in the inner loop=slow code everytime branch miss occurs