I ended up quite happy with how the lighting in this shot turned out. I used my 580EX mounted on the camera bounced off the ceiling above and behind, and a second 420EX as a wireless slave outside the frame to the lower right, bounced off the rear wall, both to create a nice bright background and to make the flowers just a little translucent. I don't often get to play with multiple flash units but this is exactly why I bought the 420EX.

Canon EOS 20D, EF-S 60mm f/2.8 Macro, f/4.0, 1/160 sec, ISO 400