May 1 is Free Comic Book Day, an event that's taken place since 2002 across America. It's just what the name says it is: a day where everyone can get a bunch of free comic books at their local shop.
All of the major players participate in the event: Marvel, DC, Fantagraphics and Dark Horse will be donating their wares to this noble cause, but some of the more interesting entities are from smaller publishers of the humor variety. Drawn & Quarterly is offering a John Stanley Library Grab-Bag, featuring reprints of Golden and Silver Age work by the famed humorist comic book writer/author. Meanwhile, BOOM! Studios, the current licensee of Disney comics in North America, is putting out a special Toy Story issue.
A full list of comics being offered is available on the Free Comic Book Day site. Not sure where the comic shop in your area is? Use the incredibly helpful Comic Shop Locator!