Ambient Occlusion Volumes
There’s a pretty cool paper on Ambient Occlusion Volumes I was reading awhile back by Morgan McGuire, the technique actually uses volumes to calculate what pixels are in a region that needs to be shaded. So no more halos and anti-halos which is fantastic, the effect almost looks as good as ray-tracing and is several orders of magnitude faster :D Though, the technique is a bit expensive for this generation of hardware; the Fermi cards from Nvidia appear to do a much better job, 35ms range for full quality. But if you don’t sample every pixel, you can get that number way down, 3-6ms range.
The reason I bring it up is Morgan has posted a sample implementation over on Nvidia’s research page here that’s worth taking a look at if the topic interests you.