In the heyday of the dotcom bubble and "free everything", Get Paid to Surf, etc., this page contained comparison listings of a variety of Free ISPs. While a few stragglers still remain, most have discovered that they can't profit giving stuff away, and have quietly gone out of business. So here is what remains, my warnings for anyone considering a Free ISP :-)

Now that the bubble has burst, and what would ordinarily be money-losing business models have become money hemorrhaging ones, there is a strong tendancy for these companies to be even more brazen and ruthless about pursuing any revenue stream they can, e.g. sending spam to their customers (or taking payoffs from spammers for same), kicking off their higher-volume or least-profitable users, sale of personal information, etc., etc. If you decide you want to go for it anyway, please read my Very Strong Recommendations below.

Free ISPs are generally "paid for" by a big, ugly advertisement bar that forcibly asserts itself on your screen while the connection is active. If the adbar ever becomes non-visble, the connection is dropped (so, no network Quake, Half-Life or other full-screen games, in other words :) So these connections are usable for Web surfing and email, but that's about it.
 
There are some services out there which supposedly offer "free" DSL service, but they have invariably been riddled with long user-screwing contracts, hidden charges, loopholes, etc. As far as I know, nobody has every walked away from one of those services with free DSL, but plenty have been scammed by hidden fees. (DO NOT give your credit card # to ANYONE offering "free" service!!!)

VERY STRONG RECOMMENDATION #1: Generally, these advertising-supported "free" services are a crafty, conniving, user-screwing bunch, and will invariably try to get you somehow hooked on *their* service (knowing you can easily find a better deal elsewhere!) so they can raise the "prices" later. If Free Webpage Providers have taught us anything, it is not to trust a "free" startup service any further than its CEO could throw a Ford Explorer ...on Jupiter. What this means is, avoid getting "locked" into a particular service (e.g. by giving out your free email address to all your friends) at all costs: DO NOT depend on them for Web hosting or especially e-mail--don't use theirs at all, not even once! Find a Web based service or other inexpensive solution for your email needs. If you do go the free-web-based-email route (most of the usual "free stuff" warnings apply), at least select a well-established service that you can live with. They will be less likely to suddenly disappear off the face of the planet and take your unread email with them, or add horrible gotchas to the service, etc.

VERY STRONG RECOMMENDATION #2: Advertising-supported service is generally a money-losing business model, and a month or a year down the road when the company itself figures this out, Bad Things can happen to the service (such as it disappearing without a trace), with or without notice. Additionally, accounts can be randomly cancelled for various other reasons (e.g. "You're not clicking on enough banners" or "We caught you trying to visit a competitor's website" or "Unlimited is only unlimited up to 10 hrs/month"), and yours could be next. This means you're f*cked, because (and tell me this isn't extremely dumb), the only way to get on their Internet service is to download their dialer, ahem, OFF THE INTERNET. This is the same level of dumbness as using AOL Instant Messager (which requires existing Internet access) to advertise AOL's internet access--but I digress. Unless you have some alternate 'net access to fall back on (such as an office connection or neighbour), have an account at more than one service, in case the worst should happen. Basically, you have to treat them the way they treat you...disposable.

VERY STRONG RECOMMENDATION #3: Remember that the legal mumbojumbo they present when you sign up usually gives them permission to do whatever they want, including limit access to every 3rd Wednesday when the moon is full, provide a list of sites you've surfed to the FBI, or send 1000 harcore porno ads to your inbox every single day. On free services, the "we can do whatever we want, and whaddaya gonna do, cry about it? Whaddya expect for free" clause is often invoked as soon as enough people are "trapped" on their service from not following VERY STRONG RECOMMENDATION #1. So, re-read it if necessary, don't use their email or sign up for anything on their service, and be ready to jump ship if they start adding more bollocks to the service than you wish to tolerate! There's no reason why, a year from now, when they "upgrade" their service so that these advertising bars takes up 95% of your screen and you have to read the actual webpage between them with a magnifying glass, you have to sit there and put up with it. Send them a nasty letter and sign up with their competitors :)
 
VERY STRONG NOT-JUST-A-RECOMMENDATION-BUT-ALMOST-A-WAY-OF-LIFE: DO NOT give your credit card # to ANYONE offering "free" service!