I've been buying used bikes for a while off of Craigslist. I started out with some old Schwinns from the 60's and 70's. The old steel bikes. They're good quality though and, if they were well maintained, still ride nice. I think the high tensile and chromoly steel frames have a little extra give to them too. Aluminum frames are more rigid. Being heavier, I feel more comfortable on a steel bike. I'm not so concerned with weight as I'm just a recreational rider and I weigh 240 lbs to begin with so a few ounces here and there aren't going to make much difference. Actually, it'll probably help me lose some weight. The old bikes don't have indexed shifting though so it takes a bit of finesse to get them into gear consistently. These are Varsities and Continentals that I'm talking about. You can find them anywhere from $20 to $200 depending on condition. I also have a higher end Schwinn from the 70's. It's a Schwinn Superior with a hand filet brazed chromoly frame. These are more in the $400-$600 range. I also just bought a couple of old hybrids which do have indexed shifters. One is a '91 Schwinn Crossfit, which was their lower-end hybrid with a High tensile steel frame but it was made in Taiwan by Giant and is actually a pretty nice bike. I bought it for $35.00 and just gave it an overhaul. Most recently was a CrissCross from '92 which is double-butted chromoly for $50.00. These are both nice comfortable bikes. If you know how to do basic maintenance and even some slightly more advanced stuff, you can find good used bikes for next to nothing. I also buy bikes for parts and then sell what I don't need. Much better way to do it than paying the outrageous prices some of these sellers on Ebay are asking. I don't want to pay $40 for a small part for a $100 bike. Makes no sense. I just wish I knew more about Giant, Trek and Specialized. Most of my research has been on Schwinns since that's what I started out with. They're a bit easier to assess than other brands because there's a ton of info online dating back to the 50's so you can find out what year a bike is, what components are supposed to be on it, how the frame was made and with what materials. I haven't been able to find nearly as much info about any other brand.