I've had great results using Dynamask. I can thoroughly recommend it. I discovered it via this guide which I found useful -
http://www.instructables.com/id/Dry-Film-Solder-Mask/I'm in the UK and ended up ordering a whole roll from a German supplier as shipping wasn't cheap and it seemed worth getting a bit more than I needed. I hope that shelf like is on the cautious side!
If anyone in the UK (or anywhere else that won't cost me loads to mail to) wants to give it a go, let me know and I'll send you some.