Pittsburgh? Everyone here seems to love the airport, but I found it pretty run of the mill. Not too good, not too bad.

I have had good experiences connecting in Minneapolis and Denver. For me, Dallas is the worst. Wayyyy too big and spread out.

Another vote for Portland, OR (PDX). Has several very nice shops, branches of downtown Portland stores, which have signed agreements not to sell their airport merchandise for more than they would in the city. If your layover is long enough, you can ride the MAX light rail line into town (who knows, maybe you'll get lucky and find a coyote on a seat, like they did a few weeks ago). There's also a restaurant with an excellent breakfast buffet (by airport standards) that actually costs a normal price. Plus, for kids, there are kid-scale models of the airport tower and a plane cockpit for them to play in. I've been stuck there a few hours from time to time and it wasn't that bad.

Baltimore - cause you can kill some time at the museum-type displays pertaining to aircraft: 2nd floor of the international terminal.