There is of course Lake Houston State Park, I know nothing about it though - never been there. Lake Livingston State Park is decent for car camping on a lake. Huntsville State Park has a small lake, some great hiking trails and is very beautiful.
A warning though, this time of year in East Texas we share our pleasure of the outdoors with some nasty insects. :mad: And we are the minority. Watch out for those pesky mosquitos, and more importantly, the chiggers and ticks.
Here is a link to check out all the state parks in Texas, maybe you can find something to fit there. The Recreation.gov site is a good place to look as well.
Texas State Parks:
http://www.tpwd.state.tx.us/park/findapark.htm
Recreation:
http://recreation.gov/advancedsearch.cfm?states=TX