I'm in the suburbs between Baltimore, MD and DC. So, we have the National Zoo run by the Smithsonian in DC and the Maryland Zoo in Baltimore. Sometimes we even go to the zoo at Hershey Park in PA. We go to zoos once or twice a year usually, event though the kids are teenagers.
We visited the National Zoo about two weeks ago, it was nice, but hot as heck (DC summers are like a special kind of hazy, hot and humid). DD13 had an overheated melt down in the otter section. She was drinking water all day, but randomly started crying because I took her picture. Had to buy her a gatorade and an ice cream to make her human again.
We visited Zoo Tampa back in April (lovely), can't wait to visit again. I expect to visit the Honolulu Zoo in August, we've been there before, it was nice.
My absolute favorite is the Oregon Zoo. Natural beauty, etc.