Okay, I discovered this great site some time ago, but for some reason, hesitated to blog about it. I guess I hate to gush over something, especially if I'm not getting paid anything for it, but it's really hard for me to be critical of this site. Comic Book Plus is a great site with tons of public domain comic material in their archive. Old comic books, comic strips, fanzines, pulp magazines, and a few other odd things are available at their site, free to read online or download. They currently have almost 18,000 books, and are adding more every day.
A lot of the material is the more obscure stuff that you've probably never heard of, but you'll also find some suprisingly well-known characters in the archive, due to carelessness or negligence or who knows what on the part of certain comic book companies. The original Captain Marvel, Plastic Man, The Spirit, Blackhawk, The Phantom Lady, and more.
You'll also find some great early work by many of comics' great artists, although unless you know what you're looking for, you'll merely stumble across them. For example, Wally Wood doing the artwork for an adaptation of one of the Fu Manchu novels, in the early '50s.
And naturally, there's much to explore for the historical buffs. See the earliest comics transition from illustrated pulps to superhero fare. Check out the wider variety of genre material from the 1950's, when superheroes were a dying fad. Horror, romance, westerns, funny animals and humor, science fiction, crime fiction, and even some decent detective fiction.
I've long been a fan of mysteries and detective fiction, since my childhood days of reading Nancy Drew and The Hardy Boys, and it's always bothered me how little detective fiction there's been in comics, at least since the 1970's, when I started reading comics. But there were more mysteries and detective fiction in the older comics. Not only were there short-lived comic book series of Charlie Chan, The Saint, and Sherlock Holmes, but there were others that were conceived as comic book characters, and not merely adaptations from prose, such as Ken Shannon, Private Detective.
Besides the large archive of a wide variety of material, the site itself has some nifty features, too. If you create an account, the site will track what you read for you, and let you create bookmarks and such. There's a forum for discussions, of course, and as I already mentioned, you can read the comics online if you want, without having to download and decompress them to your hard drive. Save the hard drive space for just your favorites.
There's probably more that I've forgotten to mention, but why don't you go check it out for yourself? You're bound to find something you'll like, whatever your tastes.