Is there a list somewhere rating the types of flooring to use over radiant heat in terms of how well heat transfers through flooring material?

I believe that Warmboard has info on different covering (for their product).

Laminate, hardwood, tiles/ceramic should be good. Avoid carpet.

Any floor can be warmed, but if you want to heat the average home with the floors, thinner is better.

Thin carpet (with thin pad), hardwood, cork, bamboo is great, and laminates that float have been popular for 20 years or so.

Naturally a stained concrete is the most efficient in terms of heat transfer and installation cost. Tile is a close second and on can't forget the potential for floor and walls for radiant applications.

As for the list many manufacturers have a list in their design manuals and...

http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=246

We have our own guide on the RPA website.

Radiant heating does not heat air directly as do more conventional forms of heating, such as baseboard convectors or forced air circulation. Radiant heat is "omni-directional." Unlike warm air, which tends to rise, radiant energy tends to travel in all directions. A large area of mild surface temperatures, such as a warm floor, is capable of transferring as much heat as a small surface area, such as a steam radiator, at high surface temperatures.

Radiant heat beneath wood flooring involves tubing in concrete, or tubing under plywood subfloors.

The best wood species for hardwood flooring used in conjunction with radiant floor heating include American cherry, American walnut, mesquite, teak and oak. Quarter-sawn or rift-sawn woods

Warmboard IS a plywood subfloor (covered with aluminum) ideal for new construction, when designed 'into' the plans - running at a cooler temperature (according to the company).