The are generally 3 ways to trigger an off-shoe flash

Wireless TTL method
Via Canon 60D, 7D, (or ST-E2) will be able to trigger a Nissin Di866 for Canon or a Nissin Di622 Mark 2. This method will need the pop-up flash which will transmitter an optical/IR signal.

Pros: TTL, no need extra transmitter/receivers.(unless ST-E2 needed)
Cons: Need line of sight, may not be reliable in strong sunlight/outdoors. Only high end flash are compatible

Optical triggers
Any camera with a pop-up flash such as the Canon 450D will be able to trigger slave flash such as the Di622 in slave mode.

Pros: No need extra transmitter/receivers, budget flash such as the Nissin Di466 and Di622 can be triggered via such TTL flash.
Cons: Line of sight preferred, manual flash.

Radio triggers
The most popular triggering option. Any camera with a hotshoe can be fitted with radio triggers such as PT-04, or the Phottix range of flash triggers. A transmitter is attached to the hotshoe or to the camera, receiver to the flash.

Pros: No need line of sight. Long range of up to 100meters
Cons: Extra gadgets needed, cost involved.

In off-shoe mode, Nissin Di622 Mark 1 can only be triggered via optical flash from a TTL flash via the pop-up flash of the Cannon 450D. The Mark 2 can be triggered by Radio triggers too.