Don't forget PTM thermal pads! They have a respectable 8 W/m•K conductivity and don't pump themselves out or dry out like thermal paste. They've become popular with gaming laptop companies and users.
8W/m.K is pitiful as they are much 'thicker' than thermal paste; good pastes should have higher thermal conductivity to boot as well. If a solid pad is needed in place of thermal paste - carbon pads, e.g. "Carbonaut" is a lot better solution. Carbon sheets have higher base thermal conductivity than copper, of course not so high when polymerized.