So what new things have we discovered:
Bosses drop bags which contain their weapon, armor, accessory and material drops which they used to drop normally previously as well as a single unique item per boss.
Eye of Cthulhu drops a shield that allows a charge that gives the player a brief invulnerability while charging. Attacks are possible with the charge, which also increases the knockback of attacks. A good, normal mob accessory.
The Brain of Cthulhu drops a croud control accessory which confuses all nearby mobs when you take damage. Very useful during invasions, as long as you can take the first attack without dying...
The Eater of Worlds drops a Scarf that lowers damage taken by 17%. This accessory will become a staple for tanky players as it greatly increases survivability.
The King Slime drops a unique accessory which makes the character the king of slimes, as such slimes no longer damage the player or recognize him as a threat. Very nice when having fun with slimes or just messing with the slime statue, but not necessary for normal gameplay.
Skelletron drops a handshaped bone thrower which shoots them in a straight line instead of an arch. Unknown if the bones thrown this way count as ammo or as thrown items.
The Queen Bee drops an accessory that makes the bees summoned by the Beesword, BeeGun, WaspGun, Beenade and Honey Cloak and variants become bigger, deal more damage and last much longer. Good if you use said weapons or accessories. Beenades plus this accessory make many enemies a bit easier to handle without danger.
The Wall of Flesh drops the currently best item, a heart that increases the number of accessories you can equip by 1. Many players might create an expert mode world exclusively to obtain this item...
Then there's the seed bag which gives you a random seed and plant upon use in low amounts.
The Fossil Armor that increases the damage of thrown weapons and allows a 75% chance of not consuming the weapon. Awesome if used correctly as well as a new class play option. Several new throwing weapons have been added to the game as well to help this class out!
Money Through, an item that summons a flying pig that acts as a piggy bank. He behaves similar to pets, but won't follow you around, may not affect pets. No longer have to carry platforms or workbenches to place the piggybank!!!!!
(Placed item of name I don't know) which acts like a magic crystal, by increases the melee potential when touched by giving a buff.
Note these are items seen that were not previously showcased in trailers or in messages by the dev team.