GearSnoop puts the iLvl number of each of your party members to the right of their portrait frame. It also puts the iLvl of any player that you target next to their portrait. If the target or party member is beyond the Inspect range the number will not show, so it is an indication of "out of range".
Version 2.1 removes the ilvl numbers when in a raid. And updates the toc to 40300.