There's also Focus targets, which are good for healers. It lets you essentially have 2 targets. It's used in conjunction with "focus modifier" so if you target an enemy and have your buddy in focus, you can run your regular attacks on the enemy, and hold down the "focus modifier" key to direct an ability (usually heal) at your buddy without losing your enemy target.
For me, Nearest Enemy, Next Enemy, Previous Enemy all work. Nearest Friend works, but Next Friend or Previous Friend don't, and "friend" appears to include NPCs. Not sure if the NPC-as-friend is a bug or as-intended, but it's not helpful.