The system floor heating the has pretty much taken over in my area is www.nuheat.com
You can get the mats in standard sizes or you can order custom sizes.
I normally let the G.C. or tile contractor purchase the floor heating systems. The reason for this is liability. If this heating system fails not only am I buying a new heating system but I also get to buy a very expensive floor. I just have my guys run a circuit to the thermostat and then run a 1/2" conduit from the thermostat box to the floor so the non heating leads can be run up after drywall. At trim out we set the thermostat.