I live in Houston and I made trip from Appleton, WI to Houston, TX and back. I also went thru Little Rock on one of the ways.
I would recommend to take scenic roads thru AR and MI if possible. I took scenic 6, if I remember correctly. I'm not sure where this picks up as I went North to South.
There are '3 sisters' near Austin which are intersecting roads that are all labeled 3xx which are supposed to be fun.
As far as TX goes, get into hill country as quickly as possible. East TX isn't exciting, in my opinion.
Arlington has a neat setup / memorial for the JFK assassination.
Waco is home of Dr Pepper.
Bryan, TX is A&M land and there is a cool bar on Lake Bryan.
Brenham, TX is home of Blue Bell Icecream, which is pretty cool. There is an airport with a 50's diner that serves the local icecream in a shake that is amazing. You can sit on a bench outside and watch small planes take off and land: http://www.brenhammunicipalairport.c...s/page0003.htm
I've mountain biked or climbed through as much as TX as is reasonable for me. The good spots tend to be where you are ending the trip, near Austin. Get some BBQ in either: Luling, Giddings, Lockhart, or Llano. Famous places are in all these cities.
Take a dip in Hamilton Pool once you arrive near the city. It will be crowded on the weekend.
A few nice parks (with camping) in TX:
PS You're gonna sweat your balls off.