The Canon WFT-E6A & WFT-E7A Wireless Transmitters allow for wireless tethering with compatible cameras such as the EOS 1D X and 1D C. Unfortunately, neither is an inexpensive accessory. However, photographer William Bennett has posted a guide for enabling wireless tethering on a Canon EOS-1D X DSLR Camera for a lot less - well under $100.00 if you already own a portable power source.
Check out William Bennett's step-by-step directions on his blog.
Tools Used in the Guide:
We haven't tested it, but a battery-powered wireless router may make the costly external power supply unnecessary. [Sean]