Kilgore - Our main rival who I never hated until they brought in dirty Coach Vallery from Louisiana who recruited kids (Toombs for example) and played kids who were then under investigation/in trouble for burglary, drugs, etc, etc. Not to mention they completely screwed us (Henderson) on their field in '98. That was the first year in like 30 years we had a losing season. 2 years before the game there ended in a brawl of epic proportions, including one of their players smashing a Henderson coach in the head with his helmet.
Highland Park - 3rd round playoff game in '92. They beat us soundly (21-7 final I think), but they had the most classless fans I've ever been around. I was actually embarrassed for them. I mean who actually throws change at a band while they're performing at halftime? A far superior band, mind you. That game makes me wish the two teams could have just brawled after the game. It wouldn't have been close.
Waxahachie - 2 playoff losses to the Indians that ended the seasons of 2 awesome teams. The '93 game in Tyler is still one of the best I've ever seen. They were #1 and we had them at the end and choked. It might've helped if we had our starting QB that game. Excuses, excuses, I know.
Pine Tree and Whitehouse - It's not football related, but I just hate them since their basketball programs were top notch and my school didn't give an F about it. Never beat either one once in high school career.