I've been playing around with screen-space ambient occlusion (SSAO) today, one of the AO-techniques used in Crysis. It's not trivial to get it to look good. I use the randomized normal trick described in the Crytek paper but I only sample on a hemisphere around the pixel normal to avoid self occlusion. I need to optimize the shader quite a bit, but so far this is just an evaluation of the technique and I'm quite pleased with the initial results.

Mandatory screenshots:

SSAO Only:

SSAO + direct lighting