This is according to a DC Comics thingy that I picked up so this has nothing to do with my opinions. I will, however, post my own thoughts and opinions on the said selections.
1. Watchmen by Alan Moore
Have not read this yes but I have it on reserve at the library so I will be reading it soon.
2/3. The League of Extraordinary Gentlemen Volumes 1 and 2 by Alan Moore
To be honest I was not all that impressed with this one. However, to be honest, a lot of times, the artwork of a comic (if bad enough) can often turn me off on attempting to really read it and this was one of those cases so it was really a matter of not really being able to get into it.
4. V for Vendetta by Alan Moore
Have not read this one yet either.
5. Sandman: Preludes and Nocturnes by Neil Gaiman
Definitely deserves to be on this list. One of the best graphic novels ever written.
6. Sandman: Endless Nights by Nail Gaiman
I don't think I've read this one yet.
7. Fables by Bill Willingham
Never even heard of it or its author.
8. Superman for All Seasons by Jeph Loeb
I just recently read this one and I was not particularly impressed with it. Surprised it made this list.
9. Superman Birthright by Mark Waid
I have not gotten a chance to read this but I really want to.
10. Superman/Batman: Public Enemies by Jeph Loeb.
It was okay. Not sure if it should be on this list though.
11. Batman: Arkham Asylum by Grant Morrison
Haven't read this one yet but I really want to.
12. Batman: The Long Halloween by Jeph Loeb Definitely fits this list. Awesome story. Another one of the best.
13. Batman: Dark Victory by Jeph Loeb I have not read this sequel to Long Halloween but I'll bet it is great.
14. Batman: Dark Knight Returns by Frank Miller
One of the 10 best graphic novels EVER!
15. Batman: Dark Knight Strikes Back by Frank Miller
This sequel to Dark Knight Returns was good but no where near as good as Miller's other Batman works.
16. Batman: Year One by Frank Miller Another addition to the top 10 graphic novels ever. In fact, this is one of those stories by which all other Batman stories should be judged by.
17/18. Batman Hush Volumes 1 and 2 by Jeph Loeb
Can't say I've heard of it but I'm willing to bet it is good considering it is written by the same guy that wrote Long Halloween.
19. Kingdom Come by Mark Waid
Another one of the 10 best GN's ever. Awesome writing. Awesome story. Awesome artwork by Alex Ross.
20. Identity Crisis by Brad Meltzer
Have not read but have heard good things about it.
21. JLA: New World Order by Grant Morrison
22. Green Lantern: Rebirth by Geoff Johns
Have not read. Probably will eventually.
23. Crisis on Infinite Earths by Marv Wolfman
I have not read the entire book but I know the story and the background behind so I am willing to bet this is probably one of those top 10.
24. Transmetropolitan by Warren Ellis
Never heard of it.
25. The Quitter by Harvey Pekar
Again, never heard of it.
26. Hellblazer: Original Sin by Jamie Delano
Have not read but might eventually.
27. Y: The Last Man by Brian K. Vaughan
Never heard of this one either.
28. Kamikake Kaito Jeanne by Arina Tanemura
Never heard of it. Won't bother reading though, not into manga.
29. Sword of the Dark Ones by Kentaro Yasui
More manga. Never heard of it.
30. Ex Machina: First Hundred Days by Brian K Vaughan
Never heard of this one either.