most of the Free games are asian grinders... and most are click to move and dont have a follow command.

Games that Multiboxing does work for that are free....

Like the guy above said... Anarchy Online is about the only one I can think of.

If you dont mind paying your list greatly increases.
Dark Age of Camelot
Ever Quest
Ever Quest 2
WoW
Lord of the Rings
CoH/V

etc etc