The Houston Zoo in Herman Park on the south side of Houston near Rice University has become one of our favorites and we try to visit every week or so when we are in the area. It really helps that we get in free under the reciprocal admissions program, parking is free, and we have learned how to take the bus and even avoid the hassle of driving.
You've seen it in the circus so go right ahead and stick your head into the lion's mouth.
While a zoo is an excellent place to see animals trying to find exhibits that are photographer friendly is much more difficult. Normally each zoo will have a couple areas to get pictures that don't just scream ZOO!
and Houston is much better than most. When the tiger is pacing the background here is plausibly natural like you could find in the wild. When he decides to take a break and lie down in the grass it is either wire mesh in the background or shooting through the wire mesh.
The meercat enclosure is another excellent photographer friendly location and I spent over 40 minutes watching these guys before Lori could drag me away. I love their antics and expressions like the guy turned saying I'm not watching you!
Many zoos are now building these free fly enclosures that allow you to be inside and as up close and personal as the birds will allow. This makes photographs against a natural looking background relatively easy. Houston has a lot more photographer friendly areas so I'll be back again and again and again.