These ratings are 2 years old, so I'm sure they've been posted before, but here goes (from Consumer Reports):

Tires with an "Excellent" rating for rolling resistance are the Michelin X Radial DT, Michelin Agility Touring, Michelin Harmony, Hankook Mileage Plus GT H707, Kumho Touring 795 A/S, Toyo 800 Ultra, and Sumitomo HTR T4. Only the Michelin X Radial DT (found only at clubs like Costco, BJ's, etc.; Costco currently has a sale going for Michelins, and all the clubs typically already have mounting and lifetime rotations included in pricing) gets their "Quick Pick" recommendation and is the 2nd best all-season tire overall.

Tires with a "Very Good" rating are the Goodyear Assurance TripleTred, Hankook Mileage Plus II H725, Yokohama Avid TRZ, Michelin HydroEdge, Dayton Grenadier PLE, Kelly Navigator Platinum TE, Goodyear Assurance ComforTred, Uniroyal Tiger Paw AWP, and Goodyear WeatherHandler LS. Of these, the Goodyear Assurance TripleTred, Hankook Mileage Plus II H725, Yokohama Avid TRZ, Michelin HydroEdge, and Dayton Grenadier PLE are recommended picks (they're the #1, 3, 4, 5, and 8th best rated tires respectively).

All the top rated tires have overall good wet/snow performance, tread life, noise, etc. so from that I'd probably just look at price and get a good deal.

They tested rolling resistance the same was as GreenSeal does, as far as I can tell, using a dynamometer.