Star in a bottle gives increased mana regeneration.
Heart Lantern gives increased health regeneration (and stacks with fire)
Dryad increases your defense, you can build a house near your arena and then move her into it
Sunflower's increase movement speed (and decrease monster spawn rate)
Honey improves health regeneration (while or after standing in it) however it will also slow you down so use wisely
Enemy Banners Provide increased damage to and reduced damage from a particular enemy.
Bewitching Table allows you to summon another minion
Ammo Box - 20% chance to not consume ammo
Sharpening Station increases armor penetration of melee weapons
Crystal ball increases magic power
Using Asphalt as the floor will give you an acceleration as well as movement speed bonus
Heart Statues connected to pressure plates can give you a quick small boost to your health every now and then
Star Statues similarly give you a small amount of mana