And then we have Jack Malone (affectionately called Lips McGee in our household, for his lack thereof) from CBS's Without a Trace. Here is one of the FBI's finest when it comes to finding missing persons. This is one show we'll watch when the pickings are pretty slim, but not a must see.
And how can we forget NBC's Law & Order's Assistant D.A. Jack McCoy. Again, the original Law & Order is not on my "must see" list, but we'll tune in occasionally (at least enough for me to note Assistant D.A. McCoy's first name).

But you can only imagine the lifting of eyebrows and rolling of eyes between husband and me when we tuned in this summer to the rerun of the first season of ABC's Lost only to discover their leading man is Dr. Jack Shepard (can't wait for that crew cut to grow out). This series is engaging enough to definitely make my weekly "must see" list. We'll see if the producers can keep this huge cast and complicated storyline contained.
So you can see the Jack phenomena spans all genre and networks. Come on guys, let's get a little bit more original - Horatio, Gil, Elliot - those are great names. Give me a call, we'll talk.
--------