I list bikes on local craigslist. I give specifics regarding seat tube & top tube length, wheel size, overall condition (ready to ride, needs work, etc). I sometimes make suggestions like "could make a great commuter", etc. Don't price on emotional attatchment of the bike. Be realistic, because almost any bike shop will sell at least a model or two at reasonable prices plus add 6 months free tuneups or something, so if your price is high then buyer would be just as well off getting a new bike from a shop.