I've recently,relative term, moved to Central Texas and heard but not tried of sone good spots:
Big Bend National Park
Guadalupe River
Frio River
Lower Colorado River east of Austin
Brazos River
Comal?

Anybody done these?

Big Bend is awesome!..We camped in the crater under a full moon and it was like being on stage w/ spot lights on you. The deer come right in the tent w/ you to see if you have any treats...We saw more wildlife there than we see in the north country....drive out into the desert at night....park and listen to all the sounds....very cool.
On a more sobering note...some friends paddled the Rio Grande and were shot at several times.

Well we started small. Town Lake/Ladybird Lake in Austin. Interesting scenery what the city backdrop and UT students. Lol. The wife and three year old did well.