While surfing the 'net, killing time, I found a place that has comic files people can download for free: www.mydigitalcomics.com. I've seen other sites that claim to have free downloads, but you have to register an account or jump through some hoops to get the "free comics". Not with "mydigitalcomics". You just go there, click the "free products" link on the left-hand side, and flip through 8 pages of free stuff, mostly comics but some magazines, too.
http://comics.drivethrustuff.com is site where you have to register an account in order to get the free stuff, but it kind of seems worth that little bit of effort because they have a pretty good selection of free books.
www.ninjaturtles.com ain't what it used to be. Since being acquired by Nickelodeon, the site has dropped all the free comics it had online. The site looks to be going through a little bit of updating, so maybe the free books will be back one of these days.
www.elfquest.com is still free, so if you're an ElfQuest fan or just want to see what it's all about, this is the only place you need to go.
Maybe I'm missing something, but "marvel.com" is just lousy with the free comics anymore. From what I can tell, they have ONE BOOK available for free. How many thousands of comics have they published since 1939, and they can't anything close to a decent selection of free books?
Over at http://captainconfederacy.blogspot.com/, the creators (Will Shetterly & Vince Stone) have made their series, "Captain Confederacy" available to read online or off (check their links).
So there you go, a few sites where you can grab comic files or read comics for free.