Any book written by Clancy himself is good, but I don't believe he actually writes any of the text for the Op Center series. I tried reading two of them; they were allright, but the writing style is very different from his other books. My bet is that he helped come up with the idea, and was paid a modest sum just to stick his name on the covers.
Like others have suggested, read Patriot Games first.
My favorite is Sum of All Fears.
Edit: Whoa, when did the member statuses change?