Haha. There are maybe 3000 separate threads on this forum about this topic. Use the search function to find anynone of them. Everyone seems to have their favorites.
All I used was the JB Learning Navigate Test Prep App for $30 on iTunes. I passed easily for NREMT-P.
National Registry is what you'll be taking, then. TX requires NR for initial certification. JB Learning (mentioned by gotshirtz) is what I see most frequently, and have heard people have good results.