Our main resource pack was updated tonight thanks to Sphenicus. If you're set to auto-download, you'll get it the next time you connect. Otherwise, you can grab it from the resource pack page. Here are the changes straight from the horse's mouth:
"Updates include some changes to paintings, a fourth song for the nether, some new mob sounds, and a lot of new fun and excitement for the End in the form of a long awaited request, including a new surprise when you leave the End for the first time. Be sure to have your music volume turned up the next time you go to kill the dragon or travel the nether rails! And remember to sleep regularly :)"