i missed an obvious one - magnets. Not the hard drive ones, which always have buyers, but ones from speakers and motors. Crafters make their projects and then stick magnets on them, to sell as fridge magnets, office wallboard magnets, stuff for kids rooms, house decor -
Magnet Boards & Magnet Crafts on Pinterest

This is a nice example of combining beer caps and magnets -
Handmade Monday: Bottle Cap Magnets | Sunday Afternoon Housewife

...and here's a magnet craft us beer drinkers can appreciate!
Bottle Cap Magnet



As far as saving beer caps, i only save the nice clean ones for the crafters. Smushed and dirty ones go in my small steel bucket.

Related to the pop top post and along these lines, i pulled only the nice clean tabs off my cans last night. Pretty sure the crafters only want the shiny ones, based on the craft photos i linked to.

Anyway, all magnets seem to be worth more than scrap.