Adafruit TO-220 Clip-On Heatsink [ADA977]
Get the most out of your regulators, transistors and other TO-220 packaged chips by clipping on a heat-sink. Your transistor or regulator may advertise it can handle high currents but when multiplied by the drop voltage, the Wattage may be too high for the bare chip! Most TO-220's can disipate about 2W's worth without a sink.
This basic, and easy-to-use 23°C/W sink will let you burn about 4 Watts of power through a TO-220 (assuming an ambient temperature of 25°C and max die temp of 150°C). No screws or thermal paste required. For more detailed calculations, check out the Daycounter heatsink calc