Melvyn Yeo's Macro Rig.
His rig consists of the Canon 5DM2, Canon 100mm L macro lens, Extension Tubes, Raynox DCR 250 closeup filter, 270ex flash and DIY diffuser.
You can check out more of his works on his DeviantArt page here and Facebook page here.
270EX on the hotshoe with a reflective board to push the light downward, and diffused by a huge concave diffuser attached to the front of the lens. No ETTL cord needed!
The foam thickness is about 3 to 4mm.
You can achieve really great light with just really simple setup like Melvyn's :), and it takes only a couple of minutes to set up!
More macro rigs here.