I guess many of us were waiting for this: the possibility to use Sigma's excellent…
YONGNUO Flash Speedlite YN600EX-RT Available At eBay ($188)
The YN600EX-RT, a Canon compatible strobe, and a strobe compatible with Canon’s new 2.4GHz RT radio system featured on the Canon Speedlite 600EX-RT, is available on eBay. The Yongnuo , the Canon Speedlite 600EX-RT for around $500. The Yongnuo is remarkably similar to the Canon equivalent.
[via DIYPhotography]