The Prius gets about 46 miles per gallon using the new American standards, which are a bit stricter than the old standards and produce lower numbers. Under the old standard, the Prius would be rated at about 55 miles per gallon. Either way, the Prius is the most efficient production car ever sold in the United States.
The first generation NHW11 was the first Prius sold in the U.S. The car has been sold in Japan since 1997. The NHW11 Prius was sold from 2001 until 2003. It had a gasoline-electric hybrid I4 engine with dual overhead cams. One unique feature on these hybrid cars is the 1 speed planetary gear transmission, which translates to no shifting... and no shift shock. That can be disturbing to someone who is used to driving hard and feeling that extra thrust when accelerating after shifting gears. Still, your passengers will enjoy the lack of shifting a lot more.
The second generation Prius, sold from 2004 thru 2007, was a complete redesign. The car is only sold as a 5 door hatchback, but this car is larger than the previous model and it offers better fuel economy thanks to better regenerative braking, which uses power from the braking process to put energy back in the battery. The 2nd generation Prius uses regenerative braking almost all the time, so that the actual brake pads rarely touch the brake rotor. Do not expect to replace a brake pad during the first 50,000 miles of use. It's very possible they could last well over 150,000 miles. We'll just have to wait and see.
For those looking for a little more performance and better looks from the Prius, there is the Prius Touring Edition introduced in 2007. It has a larger rear spoiler, better wheels, and a suspension that was made firmer to give it that European feel.
The Prius will likely expand to a full line of cars in the near future. Expect to see a performance version with a stronger gasoline engine and a super green version with a better battery and the ability to charge via a plug-in to an electricity source. Also expect to see some significant changes to the body types.
The Prius is just starting to make a presense on the used car market. Look to pay a little more for second generation models. The first place I go to look for somewhat new used cars is eBay. There are some amazing deals on there. If you're registered (it's free to sign up), just sign in and starting "watching" (you'll see the option) the auctions you are interested in. That way, you can view them all in a list and see when the auction is ending and what the top bid is.