Another vote for Kinsey Millhone. I wouldn’t mind being her.
Do meter maids count? I always liked Roxy from Dead Like Me. A tough exterior with some insecurities beneath the surface. Push her far enough and she will rip the freaking soul out of your body.
The fate-accursed Det. Diane Russell, NYPD. And Det. Laura Ballard, Baltimore Homicide. Yum!
Marge Gunderson is insufficiently hard ass? 
Literary:
Marcia Muller’s Sharon McCone
Sara Paretsky’s V.I. Warshawsky
Linda Barnes’ Carlotta Carlisle
Karen Kijewski’s Kat Colorado
Laura Lippman’s Tess Monaghan
Small screen:
Law and Order’s Lt. Van Buren
For laughs:
Joan Hess’ Arly Hanks
+10 for Lt. Van Buren
I’m really the first to mention Dee Dee McCall from Hunter? And I’ll add a vote for Lt. Van Buren.
Does Major Kusanagi count as a “cop”?
um Dana Scully???
you guys are slackers almost 50 posts with no mention of her.
Kay Howard, from Homicide. I especially liked the fact that she was always so tightly wound up and utterly convinced that no one could do things correctly except herself. I believe in one episode, her sister complains that on an overnight flight, Kay never goes to sleep, in case there’s an emergency and the captain needs help flying the plane.
That’s simple madness. Angie Dickinson was a babe and a half.
Seconded. The show wasn’t always crap, but even when it was good, Mariska Hargitay’s performance was always the best thing about it. This would be true even if she weren’t ridiculously hot.
I take it there aren’t many fans of The Shield here. Danny and Claudette are both way up there on my list of favorite tough female cops - and they’re actually believable, not generic hotties-with-badges.
Chris Cagney. Jane Tennison.