Terminals: all terminals are in one area. 44 million passengers in 2010.

Airlines: Continental: In 2012 United (Coninental) seems to have a fleet of 649 airliners based in Houston IAH. But more than half of these seem to be Embraer Regional Jets, especially the older model ERJ 145 of which there were 307 airliners in Houston in 2012.
When you count only the widebody airliners, the picture become very different:
3 Boeing 767-200, 2 Boeing 767-300, 7 Boeing 767-400 and 4 Boeing 777-200.
The Boeing 737 also seems to be very popular in Houston with Coninental (United):
99 Boeing 737-800, 49 Boeing 737-900, 31 Boeing 737G and 25 Boeing 737-500.
And Continental had their 757 in 2012 in Houston:
23 Boeing 757-200 and 9 Boeing 757-300.
In 2012 Houston IAH was the largest hub of United Airlines. (Before the merger Houston was the home of Continental airlines).

Houston is the largest city of Texas and one of the largest cities in the United States. But it's a very extended city. See Houston ... There is a tramway that follows a Main Street which connects downtown with the zoo and museum and Rice University area of Houston.