The mini map in the top right. so you can move to your friends easier when you're tryin to find them based on the street they're on. Green seems like the most logical color.
Add to this the ability to hover over a map dot and have the player's name show! Just like hovering over a street sign on the map gives the name of streets.
Ditto on the green dots and mouseovers.. I second snazzle in that I feel like I do this every day and yet every time I'm still surprised it doesn't happen..