Ah just to let everyone know (particularly the ARTICLE'S WRITER here) that Depp and Banderas would be in Sin City 3 - as in the third.
Rodriguez is preparing this as well, which will include Hell and Back, which would therefore star Depp (if he's in). Banderas would also be for that because Rodriguez wants him to star alongside Depp again (after Once Upon a Time in Mexico's success).
Sin City 2, which is the next one, focuses on 'A Dame to Kill For', which has Clive Owen as Dwight again and most probably Jolie. These two films are really connected at all, just thought I'd point it out!
In other words, Dame to Kill For = SC2, Hell and Back, Depp, Banderas = SC3.