Start saving now, the Smartcar is coming to to the US in the first quarter of 2008. This little 2-seater commuter/urban vehicle has a 64hp engine and gets 40+ mpg, better than anything available in the US. This is a bare bones commuter on the entry level (starting at around $12k) coupe; even the radio is an option!
A small, high mileage, low-impact vehicle is just what the US market needs. It will offer some tough competition to other commuters like the Toyota Yaris, and might spur other carmakers (GM, I'm looking at you) to revive some old vehicles with fresh designs and 40+ mileage.
Need a little more space than a 2-seater can provide? I'm with you, and will probably wait a few years to pick up a forfour when they become available, as they will probably be priced around $16k. Buy used? I bet these are limited production and will resist depreciation, like the Prius. We shall see.