The first Saturday in May has been Free Comic Book Day since the day's inception in 2002. Free Comic Book Day was originally started due to the new-found popularity of comic book related movies (such as Spider-Man in 2002). Piggybacking off the popularity of these movies, independent comic book store owners wanted bring new readers to their stores by drawing them in with free comics. Their promotion means your gain!
Here are some local comic book shops here in Las Vegas where you can celebrate and pick up some free comics.
Click on the store name to see what they're doing for Free Comic Book Day!