I’ve been watching the Smart Car for some years now. It’s very tiny and gets up to 80 miles to the gallon. There are several different models, including a roadster, but the FourTwo is the only one that has just gotten approval for sale in the US. It’ll go for about $14k.
The first thing people mention is “I’d hate to be in a wreck!” but they’ve worked hard to make it safe. Check out this third party test video. It’s also not as small on the inside as you might think. Here’s a commercial video.
Edmunds has done a great write-up, mentioning all kinds of great details.