Get a Sanke coupler and conversion kit. Basically it's two corny posts that attach to the Sanke coupler.
I found them at CornyKeg.com
, but I know my LHBS carries them as well, so check around. That way you don't have to change your setup whenever you want a commercial keg.
EDIT: Some beer shops that sell kegs will rent out couplers, so you might not need to buy one of those, just the adapters.