Looking very good so far! How about some sponsor decals, they're pretty safe option I think. There looks to be good spots behind the wheels, above the bumbers, and maybe some to the bumpers too. Left side of the engine hood would be cool too.
Some suggestions: The writing on the windscreen sticker looks to be straight. You could try to curve it to match the curving of the sticker. Then, your signature could be pulled down a couple of pixels, now it seems to "melt" in to the window. Also, I'd probably flip the Monster logo on the rear spoiler around, but of course it's a personal preference. Just my $.o2
