Peakguy,  The best method for rating homes would be the blower door test.  These cost from $200 to $400 and provide a list of upgrades to implement.  If these tests were standardized with a grade of A, B or C and were required to be provided to prospective buyers, it would have a big impact.  Any buyer would offer less money to buy on any grade other than 'A'.  This would get the seller to upgrade prior to any sale.  This would work for any residential home.  Commercial buildings would require some other system to measure efficiency.  

I live in a 2 story, 2000 square foot home in central Florida and have been able to keep my electric bills below $150 even in July.  Some things that I did that any DIYer can do are:

Start in the attic.  Seal all holes that enter the attic with foam or caulk.  Vents, electrical holes, fireplace and pipe chases, everything.  Seal all duct seams with duct mastic, not duct tape.  Many leaks can't be detected as they are too small.  Just seal all the seams in all the ducts.  After all that work is done you can upgrade your attic insulation and it will do some good.  

Inside your house you want to seal all the holes in the wall envelope.  That would be light fixture penetrations, vent fans, plumbing pipes, baseboard to foundation, electrical outlets, AC vents.  Use mastic, foam and caulk to keep any air from leaving the conditioned space.

Use foam weatherstriping to seal doors, attic acceses.  Seal your firplace chimmney when not in use.  

These upgrades are quite inexpensive, mainly requiring labor, but provide the biggest improvements.  The goal is to keep any heat or AC that you pay for inside your home for as long as possible.