I have six Yongnuo RF-603 (4 for Canon, 2 for Nikon, these are working with Pentax too). Works great, cheap, easy to use.
I worked with some RF-622 for Nikon but never tried the Canon version.
I've also built some DIY radio remote controller for Nikon flash (the protocol is more or less reverse-engineered), but hard to find a fast radio transmitter (without a long delay) so finally got the radio chip out from the RF-622s and use that.