Sin City is the title for a series of comics by Frank Miller, told in a film noir-like style (now known as Neo noir). The first story originally appeared in Dark Horse Presents comic book from April of 1991 to June of 1992, under the title of Sin City, serialized in thirteen parts. Several other stories of variable lengths have followed. All stories take place in Basin City, with frequent recurring characters and intertwining stories.
A movie adaptation of Sin City, co-directed by Robert Rodriguez and Frank Miller with "special guest director" Quentin Tarantino, was released on April 1, 2005. The Sin City graphic novels were reprinted with new covers and in a reduced size to coincide with the motion picture's theatrical release. Rodriguez has expressed a desire to begin filming two sequels back-to-back starting in 2007 for release sometime in 2008.
What's it worth? Take a look at this Sin City price guide: sold listings for a value indication.