I am a fan of this e-bay source:
http://cgi.ebay.com/1-4-Electric-So...tem&pt=LH_DefaultDomain_0&hash=item45f25c614e
this is what im using
http://www.mcmaster.com/#solenoid-valves/=6umpnt
5489T451
(Same as 5489T45)
Polycarbonate Solenoid Valve W/ Tube Conn Buna-N Seat, for 1/4" Tube OD, 40 Max PSI, 120 VAC
In stock at $55.20 Each
Very solid!
And simple, it has pre molded push fittings