Swords – Grants bonus stats (mostly damage, accuracy, and Counter) when you have at least one Sword equipped, as well as some special attacks that can be used regardless of weapon choice.
Axes – Grants bonus stats (mostly damage, accuracy, and Crit) when you have at least one Axe equipped, as well as some special attacks that can be used regardless of weapon choice.
Maces – Grants bonus stats (mostly damage and accuracy) when you have at least one Mace equipped, as well as some special attacks that can be used regardless of weapon choice (the knockback is especially helpful!)
Staves – Grants bonus stats (a mix of damage, defense, and wizard stuff) when you have at least one Staff equipped, as well as some special attacks that can be used regardless of weapon choice.
Unarmed Combat – Gives a ton of bonus stats (damage, accuracy, dodge, etc) so long as you do not have a Sword/Axe/Mace/Staff equipped (Crossbows/Thrown/Orbs/Spellbooks/Shields are fair game, even if you have a shield in both hands!), as well as some passive and active special attacks (including two knockbacks).
Dual Wielding – Passively removes the 36% damage penalty for wielding two Sword/Axe/Mace/Staff, and gives some stats (mostly Counter) and some passive specials. Also gives you the Sword/Axe/Mace/Staff mastery bonuses for EACH weapon; Dual Wield + Sword Mastery + 2 swords gives you double the Sword Mastery bonuses, or Dual Wield + Axe Mastery + Mace Mastery + 1axe and 1mace gives you both the Axe Mastery and Mace Mastery bonuses.
Shield Bearer – Passively gives some bonus stats (tons of Block!) and defensive specials (including a Knockback!), and some active specials. Currently works even when not using a shield; that will be patched at some point.
Berserker Rage – Passively gives some bonus stats (including Magic Resist!), and a chance when attacking or attacked to get even more bonus stats (mostly damage and armor), as well as an active that gives +100% crit for one attack.
Master of Arms – Passively gives some bonus stats (health and armor) and some defensive passives and specials.
Smithing – Passively gives some bonus stats (lots of Burliness, some Trap skill, some damage and defense) and allows you to Craft better weapons, armor, and Throwing weapons. (Crafting will be much better in the Wizardlands expansion August 1st!)
Big Game Hunter (Realm of the Diggle Gods expansion) – Passively gives some bonus stats (mostly Accuracy, also some nice Sight!), some bonuses when fighting animals, and a very nice summon. The summoned Diggles can be Butchered for meat and XP
Killer Vegan (Realm of the Diggle Gods expansion) – Gives a TON of bonus stats (33 health! among others) and some okay passive and active skills. If you perform a Melee attack on an Animal, or eat any Meat or Cheese you get some nasty long-lasting debuffs…but your ultimate skill removes all debuffs, and you can kill animals with ranged attacks and spells at no penalty. And animals will never attack you (only Counter attack if you melee them), so you can get their XP and loot quite safely
Clockwork Knight (FREE You Have to Name the Expansion Pack expansion) – Gives small bonuses to Smithing and Tinkering craft skills, and has actives and passives that scale off of those craft skills. Also has some strong melee bonuses.
Battle Geology (FREE You Have to Name the Expansion Pack expansion) – Haven’t used it yet, but it gives a variety of defensive, offensive, and stunning spells for melee combat.