Zurc's water-based/ wargames paints are formulated specifically to be used in figure-painting, and applied with a brush. They come in a 30ml bottle, and is very reasonably priced! Goodbye, overpriced paints for minis!
These paints can also work with an airbrush, though from my experience, may need to be thinned slightly.
WARNING: Even though this paint is non-toxic, please ensure adequate ventilation when painting at all times.