Belay devices are amongst the most important pieces of climbing equipment and also one of the first things new climbers tend to buy, so it pays to take some time and make the right choice. Standard two-hole devices like the Petzl Reverso 3 and Black Diamond ATC allow you to belay and abseil off single and double ropes. They're light and versatile, and equally good for sports or trad climbing, or even ice. Every climber should have one.
Black Diamond Equipment ATC Guide Belay/Rappel Device 620055