Go to any of the major employment sites and type in Houston EMT. You will find quite a few opportunities. Also do a google search for private Houston EMS and you will find hundreds of EMS services that are usually hiring.
Do a bit of research and you'll find something. Good luck.
Like Flight-LP said do your research. I was offered a transport job for a small company and had to turn it down because of low pay and no benefits offered. They didnt even offer work man's comp.
I know AMR and Acadian both operate in houston. Also check the employment listing on here. Flight-LP listed a job that sounds really interesting.