For steel, look for a sticker that has a recognizable name. Lowest grade frame I usually will consider is a "4130" frame, which is generic entry level chromoly steel, sort of the lowest end "nice" steel. Otherwise, look for brand names like Reynolds, Tange, True Temper, I****awa (sp?). A lot of time the stickers will also say "butted, double butted, triple butted" that refers to the taper of the tubing walls, esentially how heavily manipulated the tubing is. Avoid anything French, Swiss, or even Italian... Japanese bikes use mostly standard threadings that are still in use today. Brands I personally avoid are Urago, Jeneut, Renault, Peugeot, Motobecane, etc just because they tend to be French/Swiss threaded. French and Swiss are the worst to try to upgrade... they used proprietary threadings that are no longer in use. Otherwise, just about anything new will fit on just about any old bike.