DC Comics is giving away Alan Moore's Swamp Thing, Issue #1 as a PDF download. Once you get hooked, they figure you'll shell out for the print anthology that contains the first seven issues.
UPDATE: JCCALHOUN comments: "This is factually incorrect on a couple of levels. First of all, this isn't issue number 1. It is issue #21. Secondly, it is not Moore's first issue as writer of Swamp Thing but his second. His first issue was #20 which wrapped up all the outstanding issues of Marty Pasco's run which was issues 1-19 of the Saga of the Swamp Thing."
Created out of the Swamp by a freak accident, Swamp Thing is an elemental creature who uses the forces of nature and wisdom of the plant kingdom to fight the polluted world's self-destruction. Inspired by the creation of writer Len Wein and artist Berni Wrightson, Alan Moore took the Swamp Thing to new heights in the 1980s with his unique narrative approach. His provocative and groundbreaking writing, combined with masterly artwork by some of the medium's top artists, made SWAMP THING one of the great comics of the late twentieth century.