Who says you can't get something for nothing? :)
PopSci has partnered with Google to offer their entire 137-year archive for free browsing. Each issue appears just as it did at its original time of publication, complete with period advertisements. And today we're excited to announce you can browse the full archive on PopSci.com.
Not quite "free", but really good savings can be found at http://slickdeals.net/ (Some things are actually free there, but not the majority)