The only negative about Craig's List is that it's inevitable you'll get a ridiculously low-ball offer. Someone offered me $300 for my car the first day, which I turned down. Basically, have a number in your head that you'll settle for and don't take less than that. Since you know you need to payoff the car, I'd make the figure the amount you need for the payment, but list it slightly higher (like you said, it's blue book value is worth more than you owe, so I'd start with the blue book value).
I had one person ask me what the lowest I'd take was, and I was honest with the guy, and that's the person I sold my car to. He came over to look at the car, handed me $300 cash as a downpayment, and brought the rest over the following day.
Another suggestion I have is to give out a reciept if you get a downpayment to show the buyer you're serious about it. I also purchased a "car sale kit" at Staples that had a legal form for selling a car and I had the buyer fill it out with me to prove the sale of the car (and this document could come in handy if you need to prove with your visa ap where the large deposit came from!)