TB -- The Audubon Zoo is one of the top zoos in the country (top 5, I saw while searching for their website). I haven't been since high school, when the Louisiana section was brand new. If you're only spending 4 days in NOLA, that's a good place to see a glimpse into the stuff you won't experience in the city (swamps, Cajun lifestyle), in a fake Disneyesque way. I'm not a big fan of zoos, and it will be lame compared to DAK, but I really liked the LA exhibit. Of course being from Houston it's not like it's foreign to you, either.
If you're really into animals, see if you can find a public tour of ACRES. Now THIS place is AMAZING. Click this link then the link to the right that says Audubon Center for Research of Endangered Species.
www.auduboninstitute.com
I got a tour of this place when I was in vet school, and it was unforgettable for sure. It's not open to the public in general, but you might be able to call and see if they're giving a tour while you're there. They are the leaders hands-down in research for reproduction in endangered species, so your BF might be interested in the laboratory aspect of it, being an MD and all. But on top of that, it's just plain neat. When you walk in, it's like entering Jurassic Park, and I don't mean like at Islands of Adventure. You feel like you're in the middle of nowhere, but the facilities are top notch. Then when you see the animals, there aren't these huge barriers like you'll find in tourist attractions. You can feel the breath of the lions. Man, this is making me want to change my career path.
Audubon also has the Aquarium of the Americas. I've been once and don't remember a thing about it, but then I don't care much for aquariums. I'd much rather spend my time milling around a city than spending time in a tourist attraction that's similar for the most part to that found in any given city. But that's me.
I'll write more later, but unfortunatley I'm not that good at giving NOLA tourist advice since I haven't done most of the touristy stuff. I'll see if I can upload a few pics from when I visited in December, though. I did go around and take some touristy photos.
Speaking of trips... SuprGro... I'm coming to Boston next month! (Again, to see Damien Rice, the reason I went to NOLA in December

)!!! I'm pretty excited; I've hardly even been to the northeast (one day in NYC on a layover), so it's all new to me! We should meet for lunch or something. Do you know of any theatre productions or concerts that I should see April 23-26?? (ok that contradicts my "milling around" statement from before, doesn't it? but nothing says local flavor like the local arts scene)
ETA: just noticed you said a weekend, not 4 days. I don't know if I'd go to the zoo if I only had a weekend. Then again, it's not an all-day thing, either.