You probably already know about these sites, but if not -http://strobist.blogspot.com/2006/02/welcome-to-strobist.htmlhttp://www.yongnuostore.com/product/yongnuo-yn-622c-wireless-ttl-flash-trigger-for-canon/http://www.phottix.com/en/phottix-odin-ttl.htmlhttp://www.pocketwizard.com/products/transmitter_receiver/
Near as I can tell, Stobist is the guru of off camera flash. I've read through Lighting 101 and started on 102. I've learned a lot.
The other 3 URLs are to manufacturers of wireless, electronic triggers that 5D Mark IIIs will TTL control and fire 580ex IIs. I've listed the URLs in relative order of cost of equipment starting from least expensive to most expensive (I think). The URLs are direct to manufacture sites but I believe all units are carried by most major photo equipment suppliers including Amazon, B&H, and Adorama. These sites normally have reviews of the equipment also.
There are other triggers and you will find links, or names that you can google, to find information on them as you read through reviews of the triggers listed here, which I am sure you will want to do.
I expect, if an OEM hasn't already, a manufacturer to release a wireless, electronic receiver that will use ST‑E3‑RT signals to trigger 'legacy' Canon flash like the 580ex. Canon could, and should build such a device, but I'm not holding my breath.