Send an item to Trash instantly.
Command+Delete with any file or folder selected will send it instantly to the Trash.
Return items from Trash to original location.
Command+Delete with anything currently in the Trash selected returns it to the original location in the file system. You can also access this by right-clicking an item and choosing "Put Back".
Shift+Command+Delete will immediately empty the Trash. This is the safer approach since it brings up the warning dialog telling you the action is permanent.
Empty Trash without warning.
Shift+Option(Alt)+Command+Delete will immediately force empty the Trash with no warnings, regardless of what's in the Trash.