Minecraft wiki entry for Frostburn_Update, associated text: 18 new sound events, plus 2 new ambient sounds.
4 new splashes.
An "auto-jump" option (enabled by default), which automatically makes the player jump when running towards a one-block-tall obstacle.
1 new particle: fallingdust.
1 new command: /teleport.
4 new NBT tags:
FallFlying, ZombieType, ParticleParam1 and ParticleParam2.
Fossils.
5 new blocks:
Structure void, magma block, nether wart block, red nether brick (now called red nether bricks) and bone block.
3 new mobs:
Polar bears, strays (variant of skeletons), and husks (variant of zombies).