DC Comics is trying to encourage people who have read Watchmen Graphic novel to discover other graphic novels:

Five “AFTER WATCHMEN, WHAT’S NEXT?” Specials featuring a cover price of just $1.00:

• SAGA OF THE SWAMP THING #21 SPECIAL EDITION

• TRANSMETROPOLITAN #1 SPECIAL EDITION

• PLANETARY #1 SPECIAL EDITION

• PREACHER #1 SPECIAL

• IDENTITY CRISIS #1 SPECIAL (Newsarama)

Don't get too excited, these are not full graphic novels, they are promotional issues to wet readers appetites.

Identity Crisis

If you enjoyed Watchmen, I would recomend Identity Crisis:

When the spouse of a JLA [Justice League of America] member is brutally murdered, the entire super-hero community searches for the killer, fearing their own loved ones may be the next targets! But before the mystery is fully solved, a number of long-buried secrets rise to the surface, threatening to tear apart and divide the heroes before they can bring the mysterious killer to justice (DC Comics).

I loved this graphic novel.  The superhero murder mystery is very well written.  It would make a great movie to follow the Watchmen.