Aquarium World and Fish Gallery are good for sightseeing. Impressive displays, although neither is geared as much to saltwater as they are freshwater.
And both are very expensive. Fish Gallery does some pretty huge installs and maintenance for some very wealthy people. Best shop for sightseeing though.
As stated above, City Pets is good for cheap dry goods. They got new management a couple years ago and IMO, livestock went downhill, and it wasn't all that great to start with.
I have never been to Infinity or HAW.
My favorites are FJW Aquarium and Ocean Life Aquariums.
FJW is a small store in a ghetto little shopping center but Dennis knows his stuff and the place is packed wall to wall with coral and fish and dry goods.
OLA is newer and more organized and they too have a lot of nice stuff.
Both have very fair prices and are run by fellow hobbyists. Both are located pretty central to Houston downtown.
On the west side, another shop that has been around for quite some time is TNT Fish and Reef.