eBay is the place to go. The wireless triggers I have only cost me like 15 bucks. They ship from Hong Kong so they usually take a week or two to arrive (possibly more), but I've never had a problem with them.
I actually just did a search on eBay and found these: http://cgi.ebay.com …ories&hash=item2c52b7478b
These are the EXACT triggers I'm using, only this guy is in Brooklyn, so you'd probably get em in a couple days. Man, I wish he was around when I bought mine. Haha! :P Anyway, the device in the picture on the left goes on your hot shoe, the device on the right is what you mount your flash on. As long as the trigger and the receiver are set on the same channel frequency, it'll fire every time you press your shutter button. I've tested them up to 40 feet with no problems. Bear in mind though that with these, you'll have to become proficient in manual flash exposures since they don't support TTL flash metering. I've had mine for almost a year and I've never even needed to replace the batteries...and that's with sometimes forgetting to turn off the receiver and leaving it on for weeks at a time. They feel cheaply made, but they will definitely last for awhile. The awesome thing is they'll even fire Nikon flashes, which are a lot cheaper than Canon flashes 
I should also mention, if money is no object, you'd be looking for the ST-E2. It's a Canon brand wireless trigger. They can be found here: http://www.amazon.com …ics&qid=1274501857&sr=8-1
Hope this helps 