You can also go to a sign shop and just ask for scrap sign vinyl. If you tell them what you want with it (ie, you're not making signs), you can usually get a rainbow of colors free or cheap. You can also order rolls of the vinyl from places like www.harborsales.com

A little "secret" for you. This vinyl is the same stuff you get on a monokote trim sheet, but many times cheaper because it doesn't have the "hobby tax" added on.

As far as insignia and such, I've been happy with Major Decals brand for a lot of stuff. I've also made some of my own on an inkjet printer on some clear plastic I picked up at Office Depot that is meant for inkjet printers.