For off camera lighting with strobes there are several options:

• Radio Triggers
• Optical Triggers
• Wired Setup

The best solution in general is either the Pocket Wizard wireless triggers, or the Radio Popper wireless triggers. Both are highly regarded, used universally by pros and amateurs alike, incredibly reliable and perform very well. Newer systems preserve TTL data, passing the information from your camera to the strobe. Older systems were typically used with manual flash settings. These triggers also have multiple channels to prevent interference, and to create "strobe" groups.

Unfortunately, they're not cheap, nor are they really necessary for a single off-camera flash setup.

So that leaves with some other options to try.

There are ebay flash triggers, that are roughly 10x cheaper that have okay performance, but lack the bang-bang-bang reliability, distance, and features of the pocketwizard/radio popper triggers. But, for someone who is just starting out, the price point is very good.

TTL cables allow you to transmit TTL data, where as the PC cable is just a dumb sync cable. TTL data contains data to for auto flash exposures. If you're looking to do manual flash settings, then a simple PC sync cable should work.

Canon and the 550ex also support wireless IR triggering, when paired with the ST-E2 transmitter. Since this setup is IR based, it does require line of sight. It works relatively well indoors, but is not as cheap as ebay triggers.

Optical slaves trigger the flash when it detects a flash pulse. This is of no use when you use a single strobe, but in multistrobe environments optical triggers are a cost effective way to trigger them.

The big advantage to wireless is the freedom to reposition your strobes without worrying about cords. Wired setup is far cheaper, and more reliable than the cheaper radio triggers, but with the added hassle of connection.

I highly recommend heading over to strobist and going through his lighting 101 series of posts. It's incredibly informative and gives great insight into how to get started using off camera lighting.