I'd say Raleigh Grand Prix and Schwinn Paramount were really popular at that time, probably good for finding at yard sales now. I don't know a lot about vintage bikes, but I think it's harder to find parts for French bikes, so consider that if you find one that needs a lot of work. Also be aware a vintage bikes can cost as much as a new bike to build, if it needs a lot of parts. I learned this on my vintage Merckx, but it was so worth it. It's a great bike.
Here's the place to start:
http://www.sheldonbrown.com/vrbn-a-f.html
I think the price guide may be outdated, as Sheldon passed away few years ago, but it gives good info about brands.