I recently found a website called the Digital Comic Museum, which is a virtual treasure trove of FREE and LEGAL golden age comics that have fallen into the public domain. Many of these issues were pre-code, so there are plenty of great old crime and horror comics for your perusal (as well as funny animal and teen romance titles, if that's your bag).
All issues can be read online, or downloaded as .cbz or .cbr files to be read on your computer or mobile device.
You'll need to register to access the files, but it's free and easy to do so. If viewing them offline, you'll also need a comic book reader, which are plentiful on the web. I'm using YACreader for my PC and SideBooks for my iPhone. Both are free to use, but SideBooks has proven a little glitchy--just not as glitchy as the other free comic book reader apps that I've downloaded from Apple. You get what you pay for, though, so one can't complain too much.
I'm probably not telling you comic book fans anything you don't already know, but just in case, I encourage you to check out the site.
And don't be surprised if some comic book reviews start cropping up in the very near future.