Press Z to sit and stand up.
When sitting you recover your hp and mp at a faster rate.

Press Tab to toggle walk speed on and off.
This is useful to send in your summoned characters in before you attack so they can tank for you.
If you target to attack a monster from far away then move to it but are walking your summons will walk faster then you getting to the enemy 1st tanking thier aggro, and leaving your hp bar full and you free to attack.

Press the back quote (`) tilde (~) key to pick up items off the ground.

Really helpful when farming materials.

Hold Crtl to qick view item names on the ground.
Release Ctrl to turn them off.

Alt+Ctrl will enable always display item names on the ground.

Press Shift+Tab to start steam overlay.
Settings at the bottom.
A new window will pop up go to the ingame tab.
Screen shot shortcut key should be F12 click on the X it will change to none now just exit the steam overlay and it will disable steam screen shots and let you use the key normally in game without taking a picture every time.

Press O for the game options menu then go to interface, alt bar click on show.
This will give you the alt hotkeys bar which you can put your skills and items on.
Works with 1 through = keys.

You can also click on the 1 to the right of the F# keys hotbar when hovering over it to cycle up to 2 more pages of hotkeys for your skills and items.