J
josephkk
BeO, or diamond, or better yet isotopically pure diamond.
AlN isn't bad, close to common aluminum alloys.
There are some forms of graphite are better than natural diamond, but
aren't electrical insulators.
I find it more fun to actually get the numbers.
Several materials here:
http://en.wikipedia.org/wiki/Thermal_conductivity
BeO and AlN here:
http://www.aluminumnitride.com/beo-aln.htm
http://www.aluminumnitride.com/
Cheers,
?-)