A week or two ago I did a post on my first off camera flash experiment and I failed to go over what gear I was using. First item of course is my 5D mark ii. Then I need a flash, I have the Canon 430 EX (not the II), if you wanted to buy one now I would get the 430EX II Speedlite.
Next I need triggers to tell the flash to fire, mine are pocket wizards.
I have the PocketWizard MiniTT1 Radio Slave Transmitter for Canon (on the right) and the FlexTT5 Transceiver Radio Slave for Canon E-TTL II System on the left.
Then I need a light stand, flash bracket and umbrella. I have the following
Impact Air-cushioned Light Stand (Black, 8')
Impact Umbrella Bracket
Impact Umbrella - White Translucent (33")
Other than the body, flash and pocket wizards, not an expensive set up.