I don't think you can rely on brand names, unfortunately -- lots of manufacturers have made bikes with a great range of qualities, and there are lots of possible brands that could be on good bikes. I think you're better off getting to know what makes for a quality bike so that you can appraise whatever you happen to find. Luckily you have lots of good resources available to you -- check out the Classic and Vintage forum here, and do a search in its archive for similar queries. I also found the Vintage Lightweight Pricing Guide on Sheldon Brown's site to be really helpful for getting a sense of what might be out there, although it's out of date and somewhat geared to "collectibility". That said, I've never been too lucky with yard sales. Don't forget craigslist, and see if your area has a recycled bike co-op -- the latter has the advantage of coming with some help setting up and maintaining the bike. Good luck!