I have 2 ideas:
.....Idea #1.
How about a location pinger that players can use to display visible, temporary pings on teammates maps? Imagine being in a mission and getting lost but having a teammate 'ping' the map with the location of the rest of the team. I'll freely admit stealing this idea from Warcraft III, but it is something that would make life in AO so much nicer.
Teams could set rally points, point out lifts in missions, call for help at their location, and even point out loot/mobs/etc, all by, say, Shift + Right Clicking on the map. (if the ping is off the visible map, it still makes its pinging sound and maybe centers the map temporarily on the ping.
This would also help newbies find stuff in large cities as they can ask where something is and a teammember can simply ping the map. No more trying to type out complicated directions. (also, maybe there would be some way to make the ping 'permanant' like the "always up" red push pin, and perhaps even show the direction on the compass [see idea below]).
.....Idea #2.
I want a line on my compass that shows me the direction my current target is from me, much like the red line on the compass when locating a mission. The line should be a different color so they don't get confused and it would make finding teammates, Tab'd mobs, etc much easier to find and keep track of.