If you want short range line of sight wireless off camera flash with eTTL metering instead of manual metering and manual flash, you need to have a Canon commander-capable flash (like the 580ex2) or a ST-E2 transmitter (Canon or Yongnuo copy) mounted on the camera. The cheapest option is the Yongnuo ST-E2.
For longer range radio-controlled eTTL, pocket wizards are what most of the pros use.
For fully manual shooting, something like the RF603 triggers work very well.
For wired off-camera flash, just get a TTL cord, cheap and foolproof.