I've been using Duracoat this year. Insanely good stuff:
http://www.lauerweaponry.com/
They have entire camo packs which include all the colors needed and and camo pattermn templates.
They also have EZ Kits which include the airbrush and Instructional DVD.
Why go Duracoat?
1) Color matching. They match all tactical colors (i.e. Vltor Flat Dark Earth and Magpul Flat Dark Earth are actually different). 80 different colors adn counting.
2) Duracoat + Hardner is extremely durable coating and sticks to all surfaces. No need for special plastic only ro metal only paints. This will be the most durable system you can use that doesn't involve heating like powder, teflon and ceramic coating does.
3) Peel N Spray camo templates take alof the guess work out.
Camo examples:
Afghan - US 3 color Desert
Desert Storm - US 6 Color Desert Choco Chip
Desert MirageFlage - US Marine Desert Marpat
Just for example.
I'm in the middle of Duracoating a few things Magpul Flat Dark Earth just to match my FDE MIAD Grips.