I assume you mean the same power rankings they use at, say, CBS Sportsline? They rate the teams on wins, total points scored, and the "breakdown" of how they would have fared against all other teams each week.
Well, I know "sort of" how to do this in Excel...
I know how to rank each team and give them higher or lower points based on wins and points scored. I don't know how to give teams "half points" though based on a tie. Breakdowns would be a whole other sheet, but basically made off the same principle.
Anyway, I don't know of another site that does it other than Sportsline, and I don't think you can just randomly input ranks anywhere and get rankings. It's probably something someone would have to create themselves.