Here is a link that we have been using for a long time to determine what the lowest rolling resistance tires are. Thanks to Al Morrison for doing all the hard work, maybe he will come out with a new list soon? I would love to see some wider 25c tires tested, and maybe a section for lower end training tires. Also a column for the weight of the tire, including rim strip and tube for clinchers and the weight of the glue for tubulars.
This list is definitely something that any weight weenie worth his salt will look at. At this level of precision you need to start balancing the weight of the tire vs the amount of rolling resistance.