Yes, silver is king in heat transfer capabilites. I learned that in materials science class (mostly metals and composits).
However, since silver is so expensive, it's best to use silver in a paste in small amounts to transfer heat better between the CPU and HSF. See [url=http://www.newegg.com/app/ViewProductDesc.asp?description=35-100-007&depa=0[/url]
And as an aside, holy shit! What the hell happened to cheap $4 AS5???
Anyway, once the heat is transferred to the HSF, it's best to use a cheaper material to spread the heat over a lager area, thus dissapating the heat, and giving more surface area for cooling. The best common material for this is of course copper. Of course copper is more expensive than aluminum, especially to ship.