Astroworld has some rides that could definitely be construed as different. We've got the only stand up, suspended, shuttle loop, and pipeline coasters anywhere around here (anywhere in the country as far as Ultra-Twister goes). Astroworld also still has the only installation of S&S's Sky Swatter which was new for 2003.
It's probably worth your while to check out Houston's new downtown Aquarium restaurant as well (which has a number of interesting rides in addition to a ton of fish).