A Rundown of the New Features in Minecraft 1.8

Here's a noncomprehensive list of current features confirmed and experienced in Minecraft 1.8. If you have anything to add, please do so in the comment section below.

• Biomes are MUCH larger and more uniform than before.

• Swamp Biomes were added to the list of existing biomes - look for vines on trees!

• Vines can be collected with shears, in the manner of leaf blocks. Vines will grow on any surface they are placed on.
• Beef, Lamb and Chicken were added.

• Strongholds, which spawn once per world.

• Ruins, which are basically strongholds on the ground.

• Giant mushrooms, though they do not generate yet.
• Silverfish
• Creative mode, which allows flying, insta-break, unlimited items from an item palette, no damage, and more.
• Abandoned mineshafts

• Endermen- normally passive, these night-spawning mobs will teleport to (and attack) you if you look directly at them. When defeated, they can drop Ender Pearls, which presently do nothing.

• Bow charging causes ariable damage with charge, can also land critical hits. Additionally, attacks can crit if you hit a player or mob when descending from a jump.

• Sprinting allows you to run faster, and knock mobs back that are hit during a sprint- though it also appears to deplete the hunger bar faster.
• New, higher quality Main Menu

• Chest animation in which the lid opens and closes.

• Player list on SMP, as well as Server listings.
• Setting gamemode on SMP as follows: "/gamemode username 0/1", 1 being Creative and 0 being Survival.
• Hunger depletes slowly over time, which can be filled by eating food. At 9 more more bars, you will regenerate health slowly.
• XP BAR

• Eating animation
• Arrows stick to mobs.
• New lighting engine, including colored lights and smoother lighting.
• Clouds are now at the ceiling of the world.
  
  
• Cave spiders
  
  
• Zombies drop rotten flesh, which can be consumed.
  
  
• Rivers and Ravines
• Watermelons, as well as watermelon and pumpkin seeds.
• Glass panes can be crafted at a crafting table by making a 3x2 grid of Glass Blocks, which makes 16 panes. These panes can be placed in lines, corners and crosses, and they will adjoin with the nearest adjacent block.
• Iron Bars can be created by making a 3x2 grid of iron ingots at a crafting table. These can be placed in the same manner as glass panes.
• Brick, Stone Brick stairs
•  Smooth Stone Brick can be crafted by placing Stone in a 2x2 grid, which makes 4 Stone Bricks.
• F6 & F7 keys will adjust the time of day when pressed/held.

Lastly, a more comprehensive overview by the YogsCast:

New features and discoveries will be added as they are found. Stay tuned or post your own to the corkboard!