As most people have said, any bike will do (except for Lazyass, who is just being himself once again). I like the video Boondocksaints posted, not just because it covers the basic but showed a nice style of bike to ride for your first time. A step through frame with hand brakes. Retro Grouch also made a great suggestion with crank forward bicycles, something like the Electra Townie. Buy a bike that you feel you will use after you learn to ride. Good luck.

The only bike I wouldn't buy is something with a kickback brake system or commonly called a coaster brake. Brakes that use levers at the handle bars will make learning easier.