DeVilbiss Finishline 3, which is what Stewart recommends. Works well, but there is a special O ring that is easy to lose when cleaning. Replacement package of 3 or 5 (I forget which) is only a few bucks and a local auto paint store got them it for me in a couple days.
You can buy the gun online for about $150 or less. There are 2 versions, however, a water based version and a solvent version, so be sure to order the right one.