Staff Expertise - OA immunity and reach
Crossbow expertise/Wand expertise - ignore partial and superior cover
Flail Expertise - knock prone instead of sliding with a flail
Possibly Holy Symbol Expertise to prevent granting combat advantage
Possibly Tome Expertise for conjuration/summoning builds
Possibly totem expertise (ignore partial concealment and cover)
Especially for a Sorcerer War Wizard's Expertise (-5 to hit allies with AoE attacks)
For the right build Orb Expertise (+1 to push); Hammer expertise is harder but plausible