I have a 40D and one 580EX II and two 430EX Speedlites. I use
CyberSync wireless radio triggers to fire all three Speedlites when I'm doing strobist type stuff. The CyberSyncs work really well for what I do. Most of my friends use them. A few use PocketWizards but those were out of my price range. I don't know anyone who uses the Cactus V2s or V4s.