Elliot Stabler, played by Christopher Meloni. He doesn't "regularly assault", but yeah, he's got a temper. As for NE L&O, I watch a lot of L&O at work (mainly SVU and CI, because that's what's on when I'm at work), and they are pretty much the definition of straight-arrow cops. You very rarely see them do anything but play by the rules, though they'll do about anything they can within those limits, and do occasionally cross a line here and there at major story arcs. (Now, the cops of The Shield have a lot less to do with upholding the law or promoting good, but that's a different show.)
But that's why the L&O cops are good examples of paladins to me, not because they're perfect, but because they try, and get frustrated, and are tempted to circumvent the law, but are usually reigned in by their conscience. And when they're not (which happens from time to time), the fact that they win a case dirty weighs on them as heavily as losing. Early on in SVU, Stabler gets in trouble for telling a psychiatrist that sometimes, when he's alone with a perp, he wishes he could just shoot them. (There's a funny exchange later between his captain who says, "You told the police psychiatrist you wished you could shoot suspects!" and Stabler yells back, "I didn't say suspects, I said perps!") Keeping in mind that SVU deals with the molestation, rape and severe child abuse cases; wishing that the perpertrators of said crimes didn't have the protection of the law is fairly understandable. And even then, they almost always play by the rules.
There was a good line on the Closer the other day (as you can tell, I do love a good police procedural, though not the CSI family of shows), where after they couldn't make the case against someone they knew to be guilty, Kyra Sedgewick said to another detective, "We don't prosecute, we don't judge. We just find out the truth." In that respect, I think paladins have slightly less restrictions than tv cops, because once they find out the truth, they do get to judge and prosecute a little. But the truth is important, because paladins shouldn't be attacking people on a guess.
I have, perhaps, put more thought into cop shows and D&D than is really necessary, but its because I have always wanted to run a paladin and cleric -centric game that focused on the law enforcement in a large fantasy city. Law & Order: D&D. I would even love it if we incorporated the dirtier cops of The Shield, and those of the Canadian Coroner's office on Da Vinci's Inquest. But every time I mention it to players I'm met with blank stares, so I guess I'm waiting on a group who loves cop shows as much as I do. (Or they're just afraid they'll have to turn all the loot they find over into evidence. Its probably 50-50.)