In my computer, I have an AMD Athlon XP processor running at 1533 MHz, and it emits almost 60 Watts worth of heat energy when it is working. What I use to keep it cool is a ThermalRight Sk-7 heat sink, made of a copper base with soldered on copper fins.

The picture shows the video processor with its own heat sink and fan, and behind it, that fan atop the Sk-7 heat sink.

There are three main properties of the heat sink we are concerned about: Thermal Conductivity, radiation and convection. The first being how well the material transfers heat through itself, the second how well it emits heat as radiation (without a medium of transfer) and the last how well the material transfers heat to another substance, in this case, air. In practice, very little energy is radiated from a heat sink and so we are primarily concerned with how effective conduction and convection are.