Decided to add your ideas into a list
Dragon Shouts
Dragon Shout that creates an illusionary copy of you so that enemies get confused and attack the copy instead. (The World Eater)
A Thu'um Dragon Shout that sharpens your weapon. (WiselWiselman)
A Dragon Shout that swallows/absorbs other Thu'um's attacks. (WiselWiselman)
A thu'um where an earthquake starts. (shadowblood)
Spells
A spell where you can make the whole room go dark, instead of the standard "Light". (perfect for stealthy characters) (Martut)
A slow-fall spell would be great for Skyrim (it was in Morrowind), considering there are tons of cliffs. You just jump off a cliff, use it, and then take out your enemies with spells/bows all while slowly descending. (Martut)
Racial Abilites
Wood Elf (Bosmer)
A spell/ability to call animals to fight for you if you were a wood elf. (Martut)
Imperial
An Imperial ability which could only be activated once per day and it allows you to buy items for a discount (depending on player's level) for an hour. (Darkxlaser)
Special Abilities
Vampires
Vampire Unlockable Ability to lurk underneath ice in frozen-over lakes. (Martut)