Happy Birthday Party at the Office
Happy Birthday at the Office Supplies.  Fun!  This is such an easy way to let your people know how much you appreciate their hard work.  It's incredibly effective at such an incredible value.  

Quick TIP:  Why does making an office birthday celebration special become so effective for employee morale?  Because, it's not just the birthday person that gets to participate, the whole office gets involved.  Great for the team!