Some of the first places taken over by pony were Minecraft as well as Team Fortress 2. The largest MLP mod resource, MLPTF2Mods, stopped updating awhile back but has just recently come back to life with not only new content, but with a new look as well!
If you've been looking to ponify your TF2 experience, look no further!
MLPTF2Mods
Twitter: Calpain