Something similar to Ultramodern Firearms, but with Vehicles. All sorts of vehicles: From bikes to civilian cars to supertankers to millitary stuff like a hind or a tornado. With everything that smims, flies, and goes on wheels or rails.
I think splatbooks would be nice too: One for every basic class (or two of them together), with new feats, talents, Advanced Classes, Prestige Classes, equipment, and general info and advice for the class.
Maybe an equipment guide.