Farming rare items
The Jester's Cap, Prisoner's Hood and Prisoner's Tatters make rarer items drop with more regularly. You can also consume a Rusted Coin for a 300-second, 1% luck boost (hey, every little helps) and wear the Covetous Gold Serpent Ring to further raise item discovery. Magerold in the Iron Keep sells a +1 ring after you spend 10k souls on him and have the Travelling Merchant's cap in your inventory, and the the Belfry Gargoyles drop a +2 version on NG+ (bonfire ascetics don't count).
Raising equipment load
Sure, you could buy the Penal Mask off Maughlin the Armorer, but he flat out gives you the transparent Aurous set once you spend 16,000 souls with him. Both raise equip load. Effects stack with the Third Dragon Ring and Royal Soldier's Ring, so this lets you lag around rock-heavy weapons and armour such as the Fire Giant Warrior Club, Looking Glass Knight's mask, and Wicked Eye Greatshield I'm currently modeling.
The best for casters
The Hexer's Hood, which increases the number of casts for each spell by 10% and adds +1 Faith and Intelligence, is sold by Merchant Hag Melentia in The Forest of Fallen Giants after you kill Felkin the Outcast. Alternatively, buy it from Felkin himself near the first bonfire in Huntsman's Copse - you'll need 20 Intelligence and 20 Faith before he talks to you, mind. I've combined it here with the King's Mirror, which can reflect spells if you correctly time a shield bash, and the Lion Mage robes, cuff and skirt, which increases casting speed with each piece.
Also, look up the Black Hood, which Straid in the Lost Bastille hands out if you trade him four boss souls, and the Chaos Hood, which can be purchased from Navlaan upon completing his quest (or Merchant Hag Melentia after you kill Navlaan). It grants +3 intelligence.
The best for tanks
At a combined weight of 60.3. somethings (Dark Souls 2 doesn't seem to like units of measurement), you're looking at the heaviest outfit in the game. It comprises of Havel's Helm, leggings and gauntlets, and the Old Ironclad armour. Technically, the Smelter Demon has the heaviest headpiece, but I've already given it some love. Find Havel's set by unlocking a door in The Gutter with the Forgotten Key (this is obtained by killing the giants under Black Gulch). The Old Ironclad Armour, meanwhile, drops off Old Ironclads in the Forest of Fallen Giants and the Iron Keep. Goodbye, manoeuvrability.
Surviving high falls
Sweet Shalquoir lives in Majula (she's easy to spot because she's a talking cat) and sells the Flying Feline Boots for 6,000 souls. On the plus side they reduce fall damage, allowing you to drop into the deep hole in Majula without buying a ladder from Gilligan. On the downside, they're furry hot pants. Make sure to purchase the Silvercat Ring from her for 134000 souls, too, which has the same effect. All parts of the Lion Warrior set, dropped from Lion Warriors in the Shaded Ruins, also stack to reduce fall damage.