I would pay extra for some kind of Formula 1 racer, not to mention we need a car with liveries, not just bikes:
I wish the Patriot had been upgraded to at least the H3:
I see one of those on the roads lately that must be newer than the H3, but the H4 pictures I see either have truck beds or a totally different design. I'm not too knowledgeable about Hummers though (at least not the cars >_>....)
And I would just absolutely love seeing my favorite car, or as close as Rockstar could get in a roadster, the Shelby Cobra:
I know the rear half of the Stinger is similar to this one, but the overall design is too far gone from the Cobra. A company called Weineck makes a replica with an insane engine, I'm not sure if they license the original design or if the rights are expired and anyone can replicate its look (if that's the case then they could just design the in-game car to match it).