[Clippard has a good selection of solenoid valves.][1] Their line of inexpensive valves is called [mouse valves][2]. They cost on the order of $25. I've been using them for years Clippard makes other types of pneumatic hardware too: cylinders, regulators, gauges, manifolds, fittings, etc. Here are a few more manufacturers that may be instrumental for building pneumatics: [Beswick Engineering][3], [Norgren][4]. [1]: http://www.clippard.com/store/byo_electronic/ [2]: http://www.clippard.com/store/byo_electronic/byo_mouse_valves.asp [3]: http://www.beswick.com/ [4]: http://www.norgren.com/global/