Here's some third tier classes that I thought up and typed up.
Guardian- Uses Swords and Axes, The next stage of the Hero unit
Cataphract- Uses Swords, Lances and Axes, The next stage of the Great Knight unit
Fanatic- Uses Swords and Axes, The next stage of the Berserker unit
Sage Knight- Uses Swords, Lances and Element Tomes, The next stage of the Mage Knight unit
Death Knight- Uses Swords, Lances and Element and Dark Tomes, The next stage of the Dark Knight unit
Wizard- Uses All types of Tomes and Staves, The next possible stage for the Sage unit
Templar- Uses Swords, Lances, Light Tomes, and Staves, The next possible stage for the Paladin unit
Still coming up with more ideas.