Just realized how old that original post was...Container:
Large covered, heated 35-50 gallon garbage can with lid. The Brute cans are great. Get it in black if possible to absorb extra heat from the sun.
Heater:
I would use a trough heater. If you are only working with <50 gallons it doesn't need to be a very powerful one. I'm sure you could find something in the 100W range that would work.
Pump:
A small pond pump should suffice.
Restricted Drinking Area/Plumbing:
I would plumb a PVC loop out and back into the grabage can. Cut the top of of a section of the PVC pipe (make it look like a gutter) for the birds to be able to drink the water.
The tricky part with assembly will be keeping the PVC loop above the water level in the garbage can. I picture two ways of doing it. 1: partially/mostly bury the garbage can (the ground would assist with insulating the garbage can, especially if part of it gets below the frost line. Backfilling around it can be a problem though with pressure on the garbage can). 2: the loop is in an elevated area about 4ft off the ground (this would work if you have a raised coop and place the garbage can outside and run the PVC through the coop wall).