Almost hate to suggest this, but SL's /channel would be good until we get some sort of HUD mechanism in place.
Things being typed into local chat is immersive breaking.
Raycast could work too, point at an avatar and hit a key to lock onto them.
The simple example is if I have some device and wish to target acquire one of the avatars in my scene, but not type their name in chat.
So what might work nicely is
/100 target Gindipple
and this would not show up in local chat.