PHX has a couple of great spots, but since they have had a lot of construction lately, don't know how that may be today.

CLT has a great spot near the Aviation Museum. It looks like a closed dirt and gravel road, but it is OPEN. Has a great hill to sit on just beyond the glide path to the beginning of one runway. Can't get any closer than that.

I have to second the post about FRA. I get such a charge at Flughaven Frankfurt with all of the international travel and the wide variety of tail markings. Just took awhile to get over the polizei with uzi's everywhere!