Oopppsss.
Sorry David, just saw this thread.
Don't know at what stage of evolution you are in but seems your path is clear.
Few words about your flash 550EX. Though older cousin of professional flashes by two generations (Was made in 1998 followed by 580 that came out on 2004 and last, 580EX mkII 2007), is a monster flash and surly best value for the money.
One excellent choice.
It has a lot to offer once you get to know all the features. In fact a lot of billboards you have always seen and loved are made by this one. It has a lot of features and the newer versions though add more, take nothing off this ones fame and capabilities. The only problem is you definitely need more than one. Especially with their wireless E-TTL communication capabilities (Master and Slave switches are built in, you can have one set to master, attached to your camera body and have as many slaves as your need or may be as finance permits, then you can set each to one of the 4 channels so 4 adjacent photographers, or photoshooting setup in a room can coexist without affecting one another) you surely want to utilize their setup in group. Now with price of 550 at at least 1/2 (Or lesser) than 580, you can easily buy two (At least) or three to make your set up well.
If you need to see the differences between all 3 of them, check this
L I N K
but again you have all you need for studio or portable reliable professional quality flash, with the 550.
If you need of the camera flash, with all the auto functions preserved, then you need one of these
Off-Camera Shoe Cord-2 or after market cords like this:
LINK
that with 40" length wire, should give you adequate flexibility in positioning.
If you don't like to have cord but like to pay more you can have a check on
ST-E2. That is a transmitter attached to camera body, firing the 550s kept at slave mode. If you have may flashes, you can use one as master on camera but turn the firing to off, so it commands but doesn't contribute to the light on the subject from camera's angle.
Remember that Canon achieves the wirelessness by virtue of IR light not Radio frequency, possibly due to licensing problems and hassle they could otherwise face in various countries that they sell their products, if using Radio waves. So a line of sight in out door is needed. The reflective surface like walls in studio are more than enough to ensure communication between master and slave, even if line of direct sight is not available.
Possibilities are too many to tell here and you can read about them on the way as your needs demand.
Another good point about these series of pro Canon flashes, unlike Nikon's similar series that have restricted rotation to right and left, Canon's can be rotate about 90 degree on each side and more that 90 when tilted upwards. There was a very funny youtube clip in this regards, that I am not able to find it and should I get to it, will the link here to laugh.
You can use other flashes too. I believe the cheaper Sigma EF 500 DG has a very close compatibility to 5XX-Ex series of Canon flashes so may worth to have a look at that too.
Things gets a lot easier as you do the magic key thing: "Trial and Errors"