The new 90EX (for the EOS-M) is pretty interesting. The specs show it as having an AF assist beam and master capabilities. It should be compatible with the later EOS dSLR menus... Canon may have inadvertently just produced the ST-E2 replacement for those of us that can't (won't) justify the expense of the radio ST-E3 and 600RT.
This could be a nice, lightweight fill light/master for those of us still using the old IR based wireless system.
Does anyone have more info on the 90EX?