Normally, I'm the most skeptical person in the world when it comes to any "free" offer, however after a little research greatdialup.com look pretty good. The only problem that I've heard about is: "while using this ISP, a stealth analysis at Steve Gibson's site "failed" with Port 80 open. The paid ISP passed with "flying colors".

Source: http://greatdialup.com/index.php