AMBUSH BUG: YEAR NONE #1: Keith Giffen and Robert Loren Fleming return to the character they made famous (or infamous). This looks like a must-own, whether you buy the individual issues or wait for the trade.
REIGN IN HELL #1: If "Final Crisis" doesn't do it for you and you're looking for something more mystical in nature, look no further. Keith Giffen pens this story that sees Lord Satanus and Neron battling it out for control of Hell. Various mystical DC heroes are reluctantly pulled into the fight. Looks to be great.
THE JOKER'S ASYLUM: A series of five weekly one-shots that looks into the minds of five of Batman's greatest foes: Joker, Penguin, Poison Ivy, Scarecrow, and Two-Face. Narrated by the Clown Prince of Crime himself. Each issue is penned by a different writer and it should be noted that Jason Aaron (the guy who's single-handedly reviving the stale "Wolverine" series) is writing the Penguin issue.
DETECTIVE COMICS #846: Hush returns! This makes me VERY skeptical, but if anyone can pull it off, it's Paul Dini.
TWO-FACE: YEAR ONE #1: Coincidentally coming out around the same time "The Dark Knight" hits theaters. Looks interesting. And who knows? If this sells, maybe we can eventually get a "Joker: Year One".
FINAL CRISIS: ROGUES' REVENGE #1: Geoff Johns returns to the Flash Rogues. If that doesn't get you excited, I kindly refer you to "Flash: Rogue War" to see why this will be a series worth following.
Monthly comics are metaphorically more like cassette singles, whereas graphic novels are like LPs. I think there'll always be long-form trades or OGN's but I really think monthly comics are coming toward an end, at least from the big two.