The Asterisk Predictive Autodialer. Autodialers have taken new shape with the revolution in voice over IP. Here's why CallFire.com is the premiere predictive dialer on the market today:

Completely web based.
Other web-based dialers may have a web interface, but require hardware and knowledge of installing linux-based software. CallFire requires nothing more than a web-browser and a credit card.

It's easy to use. All you have to do is upload your sound prompts, use your credit card to add funds to your account, specify your campaign type, and start your campaign. It's inexpensive. At only 3.5 cents per minute, our service is one the most inexpensive asterisk predictive dialer available! No commitments or startup fees. Our service is prepaid and has no monthly minimums. Start generating leads with as little as $20.

High Volume Dialing.
If you're a big shop and require a few 1000 phone lines for your campaigns, CallFire.com is the only web-based dialer that can handle your high-volume needs. (Email: info@CallFire.com)

Easily manage multiple campaigns and statistics.
CallFire.com allows you to create and run multiple campaigns simultaneously. The interface is very intuitive and makes it easy to see your active campaigns and view detailed statistics.

Predictive Dialer Comparisons:
Indosoft Dialer - A canadian based company that, amongst other things, offers an asterisk-based dialing solution.
Vicidial - Open Source dialing software.
GnuDialer - A basic predictive dialer for contact centers. (GNU GPL)
SineApps - Acompetitor of ours with a host of features. (Unhosted)

Other Resources
Voip-Info.org - A great resource for open-source dialers.