There's an excellent brand called "sign strip" made by Spraylat that I've used quite a bit.It was made for sign painters to do complex masking and lettering.
You can spray it or brush it on, and it air dries(you can use a heatgun or hair dryer to speed it up) It's dries quick and clear, so you can draw on it with a ball point pen. It cuts really nice ,and you can get much finer detail with it than frisket.The great plus is that you can lay complicated graphics over really tricky curved surfaces( Of course, the surface has to be non- porous or it wont come off..but it works great on anything smooth; like helmets, tanks etc. It peels like frisket but you can't re-stick it.. .)
Coast airbrush sells it.
There's also another waterbased one called "Bob Dively's liquid masking film", which I havn't used yet, but it's pretty common in R.C. car and scale model custom paint circles. Most likely it's a similar product. You can find that at hobby shops.(hobbylink.com is a good one)