During the past 2 years, I have tried a number of free web hosting providers. Some of them are better than paid hosting providers. Some have really oversold their available bandwidth. Some never fix their Fantastico script, so you have to install WordPress manually. Some allow you to become a free web hosting provider yourself. Some would cancel your account if your site becomes inactive for a short while, or your site has received too few traffic. Some would ban your account for no particular reason, not sure if they also steal your content or not, lol.
Here is a list of free web hosting providers that I could say they are quite ok. Most of them allow addon domains. They are great for testing this and that. However, if you want a more reliable web hosting service, pay a few dollars and upgrade.
Freehostia – 250M disk space, 6G monthly traffic, 5 addon domains, 15 subdomains, 50 parked domains, 3 emails, 1 MySQL database, 10M database storage
Byethost – 5.5G disk space, 200G monthly traffic, 50 addon domains, 50 subdomains, 50 parked domains, 50 MySQL databases
x10hosting – Unlimited disk space, unlimited monthly traffic, 2 addon domains, 2 subdomains, 1 parked domain, 3 emails, 2 MySQL databases, unlimited database storage
Heliohost – 500M disk space, unlimited monthly traffic, unlimited addon domains, unlimited subdomains, unlimited parked domains, unlimited emails
Freeweb7 – 7G disk space, 70G monthly traffic, 7 MySQL databases
Hosterbox – 500M disk space, 2G monthly traffic, 1 addon domains, 10 emails, unlimited MySQL databases
000webhost.com – 1500M disk space, 100G monthly traffic, 5 addon domains, 5 subdomains, 5 emails, 2 MySQL databases