I admit that I keep that I keep my eyes open when I pass dumpsters. While I am not a full-on Dumpster-Diver, I won't pass up the occasional discarded treasure; particularly when it has two wheels attached.
Four times, in the past 20 years or so, I have hit the jackpot. The first treasure recovered was a French bike, a Gitane, leaned up against the dumpster at the apartment complex Val and I lived in when we first moved to Colorado. It was all there, but it had steel wheels. Still, it provided a trove of replacement parts for other French bikes which came along later.
The second dumpster bike I found was a 16" Bridgestone MB-3 mountain bike, which was missing its front wheel. Someone had put it in the construction dumpster outside the King Soopers (Kroger) grocery store, when they were remodeling. Luckily, I had a matched set of wheels from an MB-3 hanging around the house, so I reshod the bike and sold it for a bit of profit.
Not too long after that, I was shopping a yard sale in one of the alleyways of the neighborhood to my west. I looked down the alley and saw a handlebar poking up from the open dumpster. I walked down and pulled out a crappy bike (I don't even remember the brand), with a really cool set of tourist handlebars on it. I rolled it to the truck and threw it in the bed, then went back to the yard sale. Come to find out, the yard-saler had thrown the bike away, that morning.
"I would have given you five bucks for it," I told him. I hope that taught him a lesson about discarding useful things (but I doubt it).
The last dumpster bike which came my way, I found in the University of Denver neighborhood, which is unusual. So many people in that neighborhood ride that you never expect to see bikes at yard sales, even, much less in a dumpster. Most people either keep riding their old bikes, or pass them along to friends.
The bike I found was a 1980 Schwinn Cruiser 5, the classic cantilever-framed cruiser with the wide bars and balloon tires. This model also had a 5-speed derailleur/freewheel mounted on a drum-brake hub. I bought a front drum-brake hub and built a new front wheel for it, installed a retro-style parallel-leg springer fork and reproduction red Firestone bike tires, and hung it up in the shop building.
I sold it to one of the guys who works at Kaladi, a couple of weeks ago. I never rode it, and actually built it more as an art project than anything else. It would have been a killer platform for one of those 50cc motor kits...