If you want a powerful 3D painting system that supports layers, masking and adjustments you could have a look at Mari from The Foundry. www.thefoundry.co.uk/mari
@jgreasley, Can you paint outside geometry in Mari? Im interested more in new options for doing 2D concept art. If Bodypaint or Mudbox would let you paint outside geo plus use of blend modes and adjustment layers I'll check those out too. What would be ideal for me is if Zbrush would just drop it's "drop to canvas"…