An endless supply of enemies. : City of Heroes - Submissions

Instead of running around doing several missions or running around outdoors killing enemies to level, an easy trick to have an endless supply of enemies to kill is get a good indoor mission with enemies that are ideal for you to kill (least resistance to your damage type, etc). Go through the mission and kill most of the enemies- basically just do whatever you can without completing the mission, and then simply logout and log back in. Your character will be outside the mission door and the mission will have completely refreshed.