A few in particular from Morrowind come to mind.
Firstly, any of the factions which required you to defeat the leader in an Arena fight to advance to the final position, such as the Mages Guild and Imperial Legion, could be easily solved by Levitating (or even jumping) into the spectator area. Then you could just pelt them with arrows or throw fireballs at them until they die. Yay!
Secondly, the ability to push the Big Bad into the lava at the end, causing him to get stuck eight thousand feet below you, allowing you to...well, finish the main quest without a certain false-God bothering you.