How about free access to over 15,000 Golden Age Comics, including some interesting pre-code horror comics from the Digital Comic Museum?
Or if you want a great deal on something a little more recent, how about a trial subscription to Marvel Unlimited for only 99 cents for the first month?
Found via Open Culture – which happens to be one of the best resources for fascinating free public domain materials on the web. Hint: You should really subscribe to their feed. 🙂