A couple I'd like to see:
Summoner
Take the class out of Wizard and make it into its own thing. Subclasses can be themed around certain monster types as well as a Frankenstein sort of subclass who plays mix'n'match with their summons. Also, two subclasses around how the summons are used. Lacking a better name for now the first would be the Enslaver, who uses their summons for menial tasks or as cannon fodder, gets bonuses to summon's skill checks or attacks as the summoner directs/pushes them (at a cost to HP). The other, for lack of a better name would be the Befriender, who has a strong connection to unique summons and can have their summons do unusual things other summons couldn't conceive of (think Aladdin & Genie's friendship).
Necromancer
Make this a distinct class from Wizard that has some clerical elements to it. Trying to think of some subclasses - maybe one that focuses on raising/controlling the dead, another on necromatic attack spells, perhaps a third on gaining knowledge/buffs from departed spirits. Kind of a Diablo+ class, pulling in elements from prior versions of D&D (primarily 3rd).