I am in the process of building a system as well, though I am going with a 5 gallon system using the blichmann boilermaker kettles.
I haven't purchased the solenoid valves yet, but extensive research and input on this forum and other has lead me to these:
STC 2 way normally closed solenoid valve, 1/2" npt 120/60 volts AC
Essentially the same as the Asco variety, but much cheaper.
Michael