Try G3telecom.com
It's what I have used since 2004.
And you don't have to go out and buy it.
You pay online either by credit card, and you instantly have money on your account, or you can send the company a cheque or money order.
It's great, because you give up to 3 primary #'s you would usually call from, and then you don't need to enter a PIN # every time. Just dial a local #, and it will prompt you to enter the Long distance #, and that's it! (For example I have my home, cell and work entered, so I can call from there without having to enter the silly PIN# every time)
It also keeps record of all your calls, so if you ever need proof of #'s you called and since what date, you will have it.
Unlike actual phone cards, there is never any proof of WHO you were calling and dates, etc.