The Archmage is a ranged blaster with bonuses to Int skills, checks and extra boons from knowledge. Flashy booms, knows all the monsters, a better basic soulbolt, more or less.
The Champion is a melee combatant with a bit of combat maneuver boons, mobility, "hitting things dead" and bonuses to Strength skills and ability checks too.
Guardians have no Skill-boost, instead boasting a free pile of stackable Temporary HP they can replenish and reset whenever they refocus, improved reach (without a dead-zone), a shield bonus, DR, resistances, and a few ways of protecting or taking the hit for their allies.
Hierophants offer an amazing way of dealing nonlethal (only against things that it will work against!), wisdom-skill/check bonuses, channel energy, banishing at high levels, and a rather amazing ability: They pick a domain and get its powers (not spells). You can pick it every day. You can't *not* find something useful there.
Marshals require a bit more building around. The "teamwork feats" (and also charisma bonuses) role, if you don't have teamwork feats, or don't have a party really built to take advantage of them well, chances are you'll only switch to Marshals on date nights. Nevertheless, it offers several buffs and auras, and their capstone lets them bark out orders to resurrect.
The Overmind is another 'build-based' one: Most notably its own 'special bladeskill' can really make it shine. The Archetype regains Psychic Strike, item use as a psion, bigger better mindblades and some detection. Really it's not so much the minor telepathy and item-use as the boosted Psi-Likes their bladeskill gives them that really makes this an attractive choice; it's just so much less impressive without it.
Finally, Tricksters. Can you guess Dexterity? Of course. That said, they make a fine enough rogue in a way; they get magic-disarming like trapfinder gives, 'invisible' blades with improved feinting speeds (move, swift if already able to do it as a move), extra class skills with free ranks in them (again, you can pick!), sneak attack and spell-stealing.
