Well done, I especially like the GT-R background and how you spent the extra time to make the alloys look nice.
You should try a lambo, I think a new gallardo LP560-4 would look amazing in a cartoony way.
Love it. What I really loved about the Suzuki wallpaper you ended up doing was the high resolution you had available. This one doesn't look as hot blown up to 1920x1200 but still, it's sweet and I think you are doing an excellent job. I'd +rep you again if I could.