I will only mention New Base Classes usable with the Core Books:
Monte Cooks Arcana Evolved (all new base classes)
Monte Cooks Books of Eldritch Might II or Complete Book of Eldritch Might (new versions of the Sorcerer and the Bard)
Monte Cooks Book of Hallowd Might II (New Version of the Paladin and Ranger, some good thought about non Lawful good Paladins)
Monte Cooks The Book of roguish Luck (The Bandit, Gutter Mage and Shadowsworn)
Green Ronins Thieves' World (10 new Base Classes, only playable with the Core rules with some consideration)
Green Ronins Unholy Warrior's Handbook (Unholy Warrior the Anti Paladin)
Green Ronins Book of the Righteous or Holy Warrior's Handbook (an alternate Paladin, best Paladin version I know of. Now the Paladin of the God of Death is actually different the the Paladin of the God of Thieves)
Green Ronins The Cavalier's Handbook (The Cavalier)
Green Ronins The Psychic's Handbook (The Psychic Class)
Green Ronins The Nobles' Handbook (The Noble as Base Class)
Green Ronins The Witch's Handbook (guess what...)
Green Ronins The Assassin's Handbook (The Assassine as Base Class)
Privateer Press Iron Kingdoms Character Guide (Arcane Mechanic, The Bodger, The Fell Caller, The Gun Mage. I love the Gund mage flair but the rules mechanics are a not very good)