The
National Aviary is an absolute gem, home to 600+ birds! It's the only "National" Aviary in the entire country. The nation's premier bird zoo... right in Pittsburgh! (I think alot of Pittsburgh people forget about it like I do.)
http://www.aviary.org
Pittsburgh Zoo and PPG Aquarium (I think they still offer a AAA discount?)
http://www.pittsburghzoo.com/index.asp
Living Treasures Animal Parks
http://www.ltanimalpark.com
Woodland Zoo (Farmington, PA - about 7 miles east of Uniontown)
http://woodlandzoo.net
Features an extremely
rare WHITE buffalo calf! (One in 10 million buffalo are white)
150+ Exotic and regular wild animals.
(BTW: this is right next to Fort Necessity National Battlefield
http://www.nps.gov/fone/index.htm)
There are a number of
Buffalo farms in western PA if you really want to just see some wild buffalo roam. I've heard there's one up in Erie, one in central PA with a bed and breakfast in the middle, and another in Bedford County. I was travelling east along Route 30 a few years ago and was surprised when I spotted a large herd. Kinda far from Pittsburgh, but if you're travelling east...This might be it?
http://www.bedfordcounty.net/attract/bison/
And just for laughs, I thought I'd point out that there is a
Groundhog Zoo in Punxsutawney. Yes, that would be the absolutely world-famous weather forecasting Punxsutawney Phil and his phamily. There will soon be a LIVE webcam featuring Phil and his Phamily.

(Unless I'm mistaken, currently, the Groundhog Zoo houses only two tenants, Punxsutawney Phil and his partner, Phyllis.) You can always visit the Weather Center too. Hey, if you're really into wacky, unusual attractions, then you can go take your picture with ALL 32 of the larger-than-life groundhogs:
Phiberglass Phantastic Phils! Check it out:
http://www.punxsutawney.com/phils/