Well I am slowly going through instances and not all are ok to do with my setup. I use a pally/druid tank, 3 shaman, and a mage. We need to post which instances are multibox friendly.

So far the ones I am able to do are;

Steamvaults,
Sethekk Halls
Old Hillsbrad
Mana Tombs
Slave Pens
Underbog
Ramparts
Blood Furnace

Note these were done without a full DPS 5 shaman group. A full dps group should be able to do more than a tank + dps healer group.

The Instances I cannot do at the moment are:
Crypts
Mechanar


I still have several instances to try but so far those two are impossible to multibox. The mechanics are just too much of a PITA for my tank + dps healer group.