I love my Taurus 24/7. I have never had any problems and it shoots great.

There's so many different makes and models out there.What I suggest is shop around and handle as many as you can.See which one feels right to you.Personally for a carry gun I wouldn't skimp bybuying a lower end gun. Your life might depend on that gun. If it malfunctions at the range is one thing. In a SD situation you need a reliable gun.
I carry a Glock M-27 which has been nothing but reliable. They have the same gun in 9mm the M-26.They would fall in your price range.As for buying new or used depends on allot of things.The condition ,price and the source.I sure wouldn't buy one off the corner,just because.

Good luck in your decision.

Check out the beretta storm px4 pistol. I bought one a couple years ago, and love it. Has 17 or 20 round mags, great ergonomics. All the bells and whistles, interchangable backstraps, light rail, night sights, etc... I have owned many other brands, but it is hard to beat berretta. They make a nice little compact model now also. http://www.px4storm.com/index.aspx?m=53&did=55

For 600$ you should be able to get a glock 19 withan extra mag(total 3)and some ammo. They are a good gun, I have to go out and buy one for the wife shortly.

CZ 75B

I bought one of these for my son when he starts shooting IPSC matches with me. Nice pistol, but, in dire need of a trigger job. (And, under $300... ) As I shoot in competitions, I'm VERY partial to single action semi-autos. You couldn't give me a double action (i.e. Beretta, S&W, etc., etc.) or safe action (Glock, S&W M&P, Springfield XD). Well.... you could give it to me, but I'd trade it in for a single action.

I bought a Taurus Millennium 9mm about 6 years ago and it has functioned flawlessly. I have put about every conceivable brand and weight bullet through it and hundreds of reloads. Never a hiccup.

I carried it concealed until all the time until I got a P3AT. I now carry the P3ATwhen Iwearshorts and a t-shirt since it is practically unnoticable and the Taurus the rest of the time.

Springfield XD....most accurate 9mm I have ever worked with.

If your still in the market for a reasonably priced 9mm,Check out this site: http://www.centerfiresystems.com/index.asp?PageAction=VIEWCATS&Category=233$349.99

I have the 9mm MAP 1 FS. It's a bit heavy for carry but a great shooter. I use it in IPSIC & IDPA.
Their poly frame would make a good carry gun though.

-al