I am shocked to read Brandon say something nice about Astroworld! Pigs are flying!
Anyway, Texas is a big state with a fairly large number of parks with rollercoasters: Six Flags Over Texas, Fiesta Texas, Astroworld, Sea World of Texas, plus Wonderland and Joyland (these two are a bit harder to visit). Just hitting the three Six Flags you'll find a number of great rides such as Texas Giant, Superman Krypton Coaster, Texas Cyclone, Ultra Twister, Titan, etc. If you wait till 2003, who knows what new rides will have been built.