Burt's meat market at 5910 Lyons Avenue. I am not kidding when I say they have boudin as good as any in Louisiana (well, any I've had). http://burtsmeatanddeli.com/ Not really in Katy, but worth the drive.
El Tiempo market on Washington has good marinated fajitas the butcher guy doesn't speak any english, though, so hopefully you can mix in a few spanish words for him