The Mrs. was lamenting the fact that they'll never get actors as good as Woody and McConaughey again -- whereas I was pretty sure that after the insane buzz of the first season, the producers could pick up the phone and get almost anybody to sign on. But to Belgian Guy's point -- that does raise the specter of picking a big name just for the name. That said, I think Brad Pitt is actually a pretty good actor.
Well the showrunner has heavily hinted at the fact that at least one of the detectives will be female in season two, so... Many people have suggested Catherine Keener for that role.
The list of female A-listers (or something in that general ballpark) whom I could see playing a detective is actually rather small. Amy Adams maybe? I guess Theron wasn't bad playing a cop "In the Valley of Elah". Though if that means she would be interesting to see as the lead on an eight hour mini-series... The amount of attention and goodwill this show gave Wooderson - right around awards season as well - will be something other movie actors (and their agents) will covet though.
My favorite female TV cop is detective Deangelis (played by Inga Cadranel) on "Orphan Black", but she is about four rungs too low on the fame ladder to even qualify for the female detective role on TD.
Some good suggestions Crimen, but it is interesting that apart from Hilary Swank, none of them approach Wooderson level fame.