Press ctrl+f2 to max out a stack of whatever your cursor is over in your inventory. You must have hovered over something before enabling this cheat.
Fullbright: all tiles will be fully lit.
Exposing a bunch of player variables - change or freeze your health, breath, mana, position, defense, modify the stats on any item (put it in slot one and use the exposed fields), change a log into a dungeon key, make yourself immune to freezing/stoning/webbing, etc.
Expose a bunch of system variables - change the time of day, spawn invasions, etc
Craft Anything: craft anything, any time, any place - no need for materials or crafting stations.
Force Obsidian Skin - lava does no damage
Extend reach: allow interaction with blocks/doors/switches/etc from 10 times as far away. Also expose a variable that allows you to change the grab radius.
More minions - change the max number of minions you can spawn.
Force Prefixes - always get warding accessories, legendary swords, unreal bows, etc. Also, works great to enable prior to new world generation for stocking chests.