Back in the old days, we scrounged parts to make our fixies. Armed with advice from Sheldon Brown, the Obi Wan of the fixie movement, I converted an old Peugeot PX-10 into a fixie and rode it damn near everywhere. I later replaced the PX-10 with a fixie Merckx that I also managed to put quite a few miles on. Bikes come and go in my life, but as near as I know both machines are still rolling down roads somewhere. And pretty much anywhere you look these days, you'll find fixed gear bikes.
Now, you don't have to build your own fixie. You can walk down to your local bike shop and buy one ready to go. The bike pictured here is the Trek Earl. I'm probably biased by working in a Trek shop, but I think it's pretty cool. The bike comes stock with a flip/flop hub so you can ride it either as a coasting single-speed or a true "it only goes when you pedal it" fixed gear. The dual top-tube not only looks funky, the gap is just the right size for carrying a U-lock. I also like that the bike doesn't fall for that "I don't need brakes" fashion and it's got decent clearances for fat tires and fenders if you want to go that way. You can even put a rack on it. It's a good, simple bike for well under $500.