The best decal paper is from Micro-Mark
www.micro-mark.com and is quite reasonably priced, but you have to fill up a sheet of decals first, otherwise you are wasting it. They have both inkjet and laser paper, and they have the white backed paper, so your inkljet printer just leaves any white in your decal blank, thus all other areas on the page are colored, and the white remains white. You can also get clear paper for all decals that don't have white on them. The paper is about $7 for 5 pages and you can order online too. It's amazing what else they have there, an amazing source of hobby tools etc. They send a catalog out with every order, so take a look.
One thing to remember is to use a setting solution like microsol to make the decals more flexible and conform to compound curves and panel lines etc. If you have a half decent inkjet printer (and most are now) you can make really professional custom jobs, and you can also get most logos etc. already made up on the net. Anything you can't get off the net (for example, I am doing the Sabre El Diablo devil), you can do yourself with corel draw or photoshop.
If you aren't sure, $7 isn't too much to have a go and make your own, you won't be sorry. And if you are, you can make up some great decals for the kids, they go great on lunch boxes, doors etc.
Tim.