All the entities in my Minecraft game (mobs, chests, the player) have this problem where the faces of the entities will twist to the wrong corners of the cubes, making it look like they've collapsed in on themselves. I don't use mods and the problem persists with or without texture packs.
Added (1). Tried deleting.minecraft and it doesn't seem to work.
Try doing a clean reinstall. To do this: delete your "bin" folder in your.minecraft, along with options.txt.
You will loose no saves or resourcepacks, but all your settings will be reset.
First, back up your worlds. Go to Run, type in %appdata%, click on.minecraft, then go to saves. Copy the saves files somewhere else. Then go back to delete.minecraft.
Then reboot Minecraft.