I've had a tutorial up for using the wireless flash system that Canon has built into their flashes, but ever since I got myself a 7D, I've been telling myself that I should expand that tutorial and include instructions on how to do things now that Canon's new cameras can use the pop up flash as the master.
So, if you go and have a look at the tutorial, you'll find it has been completely updated and revised, with a whole lot of new information! Now, if you have a 7D and a single flash, you can enter the wonderful world of off camera flash and take your photography to a whole new level!
You can read the tutorial here: http://tiberius47.devia