Check the components if they are still on the frame. Shimano on OLDER frames is usually a good sign, as is Suntour. I can usually tell from the way the crank is connected to the chainwheel(4-5 hex bolts), if its like that on an older bike chances are it was pretty good in its day. Always look for lugs on older bikes and of course butted seamless tubing. Pick it up, is it light AND steel? Stay away from aluminum, while lighter it wont last you as long, and its already old and used. Someone forgot to say Bridgestone, shame on you. I agree also with Panasonic(yum), some Fujis, higher end Schwinn, all relatively common second-hand. For really cheap frames hit up flea markets in your area. You may have to be religeous for a couple of weeks about it, but they always have steals. I got an old Fuji frame for $3, still had most of its components on it too. I found an old beater Schwinn with good cranks still on it for $5. Thrift-stored an almost new shimano cassette for $5 on a bent wheel. By the time I was done the most expensive part on the bike was the $10 chain I put on it, and I spent less than $50 to have an awesome bike.