For me, accessibility trumps literature. I would rather have a comic book that is read and enjoyed by any person who would not otherwise read a comic, inspiring them to pick up more comics. For that, I would go with:
Planetary
Marvels
We3
Liberty Meadows
Pride of Baghdad
Shockrockets
all those coffee table books that DC produced (Superman, Batman, Wonder Woman, Shazam, JLA: Heaven's Ladder)
Once you have drawn people in with easily accessible comics, I think you can show them the denser and complex comics like:
Watchman
Planetary (yes, again)
100 Bullets
The Walking Dead
All-Star Superman
Preacher
Batman: Year One/The Dark Knight Returns
Daredevil (Frank Miller & BMB/Alex Maleev run)
Obviously, I don't know how much they would take off, but I personally love and would highly recommend:
X-Men: Mutant Genesis (issues 1 to 3)
Marvel Boy by Morrison and Jones
Earth X
Daytrippers