NetZero - Free Internet for up to 10 hours per month. I find it ironic that they keep the name NetZero even though it costs money for their real service.
AOL - Free for 1000 hours. Requires a credit card. If you play your cards right, you can get months of free service by canceling before your time expires and then signing up when they call you. I once got an entire year free.
Address - I've heard nothing but bad things about this. Free internet, but they interrupt with commercial breaks instead of a banner.
Internet4Free - No banner ads, no interruptions. The catch? You must maintain an e-mail account, and agree to their terms of service which states, and I quote directly from the site, "Affinity Path has no obligation to monitor the Service, but may do so and disclose information regarding use of the Service for any reason if Affinity Path, in its sole discretion, believes that it is reasonable to do so, including to: satisfy laws, regulations, or governmental or legal requests; operate the Service properly; or protect itself and its Members." Besides this, they sell your real e-mail address (the one you sign up with) to spammers. Their privacy policy is either hidden or non-existant. They briefly metion it in their Terms of Service section, but don't link to it.. I can't find it, but I'm sure it's gets a lot worse. If you're desperate and don't want an ad bar, sign up at your own risk.
Hotmail - I like Hotmail and use it myself. Easy to use, and they offer many spam filtering options. There are three versions. A free version, an upgraded version, and an even higher version. Each step up equals a larger file storage in the in the inbox, and the ability to send and receive larger attachments than the step before it.
Yahoo Mail - Yahoo Mail is about as popular as Hotmail and about as simple to use. It is also free, although they have an optional subscription service that gives you more space and allows you to send and receive larger attachments than the free version.
Mail.com - I believe they still offer free e-mail service. I was never impressed with the quality of the site anyway. Give it a try if you want something new.
Sneakemail - This is a very novel idea. Sneakemail gives you the ability to create disposable e-mail accounts. In fact, you an create an address for each person you e-mail. If a spammer catches hold of it, all you do is delete the address and make a new one. It's a bit complicated, but if spam is a big problem, you may want to take it for a drive.