i'd say the duo of darelle revis and antonio cromartie is the best in the league, because they get help from a better overall defense.
the second best duo would be leon hall and jonathan joseph...if the bengals had a better pass rush, they might be the best duo, but the gap in between them and revis+cromartie is slim.
then, i'd go with charles woodson and al harris...but like rossibreath said, tramon williams has done a good job filling in for al harris.
terence newman and mike jenkins have also done pretty well for the cowboys, but this year, jenkins has been committing too many penalties.
surprisingly, fabian washington and chris carr have been playing pretty well for baltimore, i thought they'd be a huge drop off after the ravens no longer have chris mcalister and samari rolle...it'll be interesting to see them now with ed reed coming back.
but as previously stated, the titans, dolphins, redskins, panthers and steelers also got some good cornerbacks. the titans' rookie cb alterraun verner from ucla is gonna be pretty good...