I just wondering who else out there uses their third valve for A above the staff and/or low E. If you do, what kind of trumpet do you play on. Thanks

It really depends on the fingering pattern of the part/piece I'm playing. Rimsky-Korsakov's "Flight Of The Bumble Bee" is probably the best example. I know there are many others, but none are coming to this old mind at the moment. I've used it a lot doing improv, too.