Wrens are small, chunky brown birds with a slender, slightly curved bill. Many have a cocked tail. They are very curious, and have a loud song.

Carolina Wren (Seen in The Woodlands, TX)

This little bird has a HUGE (and varied) song, and sing year-round. He forages everywhere, it seems, investigating every nook and corner for insects and spiders. The Carolina Wren doesn't migrate, and pairs of wrens stay together all year on permanent territories. After breeding, the immatures tend to wonder further and further north. We have noted that this delightful bird will forego a pretty birdhouse for a potted plant of a BBQ grill for building their lovely cavelike nest! 
Cactus Wren
Cactus Wren - We found this guy in Falcon State Park (near the Rio Grande), Texas. This wren is quite large (over 8"), but that eye-stripe going clear across his forehead convinced us that he wasn't our familiar Carolina Wren on steroids!

This is the Cactus Wren's nest in the photo above.  It's almost the size of a football!

Bewick's (pron. Buick's)Wren
When we went to my brother's house just west of Austin, we found similar (but different) birds. In this case, the Bewick's Wren looks very similar to our local Carolina Wren. While the western counterpart of the Carolina Wren, it has light under-parts and white tail edges, which distinguish it from the other.
House Wren
This bird is a spring and fall migrant throughout most of Texas, and spends the winter except in the very northern parts of the state as it eats spiders and insects during the winter.

This wren is brown with just a faint stripe over the eye, and none of the other facial stripes that other wrens have. Usually his tail is cocked over his back.