Andertoons - The Cartoons of Mike Anderson
http://www.andertoons.com/free_cartoons/
This site offers a free daily cartoon in a variety of topics from business to sports and technology. A smaller version of the cartoon appears on your site. When visitors click on it a larger version appears in a pop-up window so visitors are not taken away from your website. A demo is provided on their site.

ARG! Cartoon Animation
http://www.artie.com/cc/link-random-anim.html
Free animated cartoons are offered here for both free and commercial websites. Animations change with every visit to your website. Themed animations run on a seasonal schedule (New Years, St. Patrick's Day, etc). Samples and demos are provided.

One Stop Cartoons
http://www.reachone.org/pages.asp?pageid=52438
Comic strip that is free and updated weekly. Some great content here and easy to implement into your site. A few lines of script and you're up and running.

NewsletterCartoons
http://www.newslettercartoons.com/freedaily/freedaily.cgi
Another site with some excellent content. Daily business cartoons are offered free, but you must provide them with your email address and the site you intend to use the material on.

Comic Exchange
http://www.comicexchange.com/
A cartoon served up daily. They also offer an ad exchange program that includes 1,000 free impressions when you sign up.

Cartoon Strips
http://www.wdvl.com/Authoring/Design/FreeStuff/Cartoons.html
A few different cartoon types are offered. No forms to complete, just copy the HTML code provided and paste it into your webpage. Most of the cartoons are updated daily.

Frenetic Wanderings
http://www.freneticwanderings.com/webmasternotes.htm
Daily and weekly rotating cartoons. The daily version is basically a "best of" while the weekly is mostly fresh material. No charge for personal or free sites. Nominal fee is required for commercial sites.

Off the Mark
http://www.offthemark.com/affiliates/affiliateinfo.php
They offer a free weekly updating cartoon for your website. Each cartoon includes offers from their webstore, and you can sign up as an affiliate (CafePress Affiliate Program) to earn income from sales generated from the webstore link in the cartoon.

CartoonFeeds.com
http://www.cartoonfeeds.com/
The color cartoons are hosted by Giggleguts.com and change every weekday. You have to provide them with your name, email and website URL to obtain the code.

Lethargic Lad
http://www.lethargiclad.com/license.htm
Comic strip with a new weekly episode that appears every Sunday. Not sure of the history but it looks to be a super hero or science fiction type theme.