I purchased the HobbyCNC PRO Chopper Driver Board Kit from HobbyCNC. The price was good and delivery was quick. Kit went together with clear assembly instructions.
HobbyCNC has a new board, with fewer features that would most likely work just as well: HobbyCNC EZ Driver Board Kit. $64 vs $79.
I managed to blow one of the driver chips, though I tried to be ultra-careful. I replaced the chip, added a big heatsink, and all is now good.
Here's the bare board. The quality is first-rate, as are the assembly instructions. Take your time, double-check everything.
I checked every solder joint under an inspection microscope - my soldering skills are excellent, however my eyesight is not.
Pay attention for any solder bridges or cold-solder joints.
The completed board "in action". For the heatsink, I used the same material that was used for the linear bearings and the rails. I put some heatsink paste between the driver IC's and the heatsink. I'm sure all the sawdust isn't ideal, but I'm not done yet!