so I get asked a lot 'what brushes do you use?' and I thought I may as well put this up. There's actually only one brush here, but to get the different angles all you have to do is adjust the angle of the brush; making the brush tip rounder will, obviously, round out all the strokes, but leaving it at around 60% roundness can still give a nice variation in size.
EDIT - I cannot for the life of me remember where I got this other brush so if anyone knows let me know and I'll replace this with a link, but for nowthe splodgy brush is the one I use for the majority of my ' painterly' work, and it works especially well for smoke and clouds
EDIT - Added the basic square I use, just in case people want it.