The current issue (April 09) of Metal Architecture magazine has an interesting article about Above Sheathing Ventilation (or ASV).  Now, the article is aimed at the metal construction industry, however, this would seem to have a direct connection to several recent threads on this forum. 
The article was written by a marketing VP for the company making one of the products discussed, so his opinion might not be totally objective.  However, the testing numbers quoted are atributed to Oak Ridge National Labs, so they should be verifiable. 
In essence, the system allows for the ventilation to occur between the steel roofing and the roof sheathing, allowing for up to 30% reduction in the amount of heat passing through the roof assembly.  Now I haven't checked out ORNL for more info yet, but I think it deserves a look.
Thoughts, comments, or further information is welcome.

Wes,

Did you see a web site for the ASV?

Alton,

The product used in the article was made by Roofhugger (www.roofhugger.com).
However, I don't think that particular product is shown on the website.