I have heard about other places, but I really try not to dive in freshwater, unless it is in the Cenotes in Mexico.
You should probably limit your recommendations to the Riviera Maya, then, huh?
Clear Springs is about 45 minutes east of downtown Dallas. It's an old limestone quarry with a few boats and an airplane fuselage in it. It also has a nice rock wall and some hydrilla covered flats. It's a good way to kill a day. A lot of us dive there pretty regularly. Let us know when you're in town and chances are we can meet you out there for a dip.
I've been to Athens once. It's about an hour and a half southeast of downtown Dallas. It has a lot of junk in the water in the way of sunken boats, buses and airplanes. It has absolutely no life in it. No plants. No animals. As soon as anyone touches down on the bottom, viz goes to hell. You will spend hours cleaning your gear afterwards. There are a few shops that take classes down there. If you live in Athens it might be worth a try. If you have to drive more than 20 minutes to get there, probably not.
If you are in town for more than a few days and would like to venture out a little, there are very nice dives to be had at Possum Kingdom Lake west of Fort Worth but you may need to rent a boat. Lake Murray in south central Oklahoma and Broken Bow Lake in southeast Oklahoma are both worth a trip. In my opinion, Broken Bow Lake is an overnighter. There are very nice camp grounds there and cabins for rent as well. The dives are really good, though.
A long day or overnight trip to the south can put you at Lake Travis near Austin. Very pretty country and some really nice guys to dive with down there.
You could always head to Houston and out into the gulf for a 3 day live-aboard to the Flower Gardens or to South Padre to dive the Texas Clipper if you are like our friend up there who won't dive freshwater.