I have ended up owning a bunch of drip tips. It isn't really something I think of as a collection, though. One or two of my favorite vendors have free shipping when you spend 'X' amount of dollars, so whenever I'm a couple of bucks short of the free shipping, I'll add an atty or a couple of drip tips.
I'm with cskent - I own a few metal drip tips and I even used to prefer them until I burnt my lip one too many times. I've had some glass ones but they break easy. A cheap delrin or acrylic drip tip is usually the ticket. Or, just as cheap as delrin (at one vendor anyway - twice as much at another), I've become pretty fond of ceramic drip tips for the same reason I like delrin or acrylic. They don't get hot.