Guardian - Heavy armour tank, soaks up damage and pulls aggro, can self-heal, average melee dps.

Champion - Best melee DPS, can go AoE or single target. Has off-tank trait line, but its not good, especially compared with Guardians and Wardens.

Captain - Buff and healer with pets and average melee DPS. An essential part of any major instance/raid.

Burglars - melee DPS and Debuff that can stealth through areas. Underappreciated by most players

Beorn - melee DPS/support/off-heal class, changes from man to bear.

Warden - DPS/tank class that uses javelin and complex gambits. More complicated than guardian, but can be OP in the right hands.

Hunter - Ranged DPS, can set traps that damage/stun enemies and CC

Rune-Keeper - Magical DPS/Heal class. Fire damage RKs deal OP damage right now (so may be nerfed soon).

Lore-master - CC/Debuff/Support class with pets. Pets are pretty versatile, so LMs are useful in most situations

Minstrel - Healing/Ranged DPS class with musical instruments. Can one-shot kill most landscape mobs, usually used as healers in group content