Mine just changed since I just finished Watchmen and that's now made the list.  So here's mine, in no particular order:

1. Watchmen
2. Johnny the Homicidal Maniac
3. Batman: the Long Halloween
4. Sin City: That Yellow Bastard
5. Sin City: Hell & Back

1) Rurouni Kenshin

2) X-Day

3) Trigun

4) Chibi Vampire

5) Samurai Deeper Kyo

So far I'd have to say those have consistently remained my favorites. :)

1. DEFINITELY the Sandman graphic novels by Neil Gaiman at number one! Best ever!
2. Lucifer, by Mike Carey
3. The Crow, by James O'Barr, a classic
4. V For Vendetta, by Alan Moore
5. Fables,  by Bill Willingham
6. The Walking Dead, by Robert Kirkman

Hmm, that is all I can think of at the moment. There are more. I am actually planning to read Watchmen, but havent had a chance yet.

1. Red River by Chie Shinohara
2. ElfQuest by Wendy & richard Pini
3. From Far Away by Kyoko Hikawa
4. Y: The Last Man by Brian Vaughan and last but Not least.....
5. Fruits Basket by Natsuki Takaya   Those are by far my favs hope there helpful!

1)  Watchmen

2)  Imadoki

3)  Rurouni Kenshin

4)  Death and Return of Superman (omnibus)

5)  Alice 19th

I haven't actually finished a lot of the manga series i've started yet... so although I've had exposure to reading many different series, I don't feel qualified to rate them if I haven't finished them yet.

I will say that Death Note is by far the best manga I've read yet.  The plot twists and amazing artwork were continually a source of inspiration to me.  I hated the ending and didn't think the manga-ka stayed true to character with Light Yagami's words/actions at the end, but still, it didn't ruin this for me.

I love Death Note, too!  But I didn't read the manga, I watched the anime.  And, from what I hear, the manga has a waaaaaaaaaaay better ending than the anime does.  But I liked it anyway.  I've seen a lot more animes than I've read mangas (just started a collection) but I've been reading Superman comics/omnibuses for years and I've read Watchmen some time ago.  Its TOP OF THE LIST material!!

1. Mouseguard
2. Yotsuba&!
3. Cafe Kichijuji De

Others to be named later

1. Veils by Pat McGreal

2. Buffy: Season Eight

3. The Girl Who Would be Death (Sandman Spinoff by Caitlyn Kiernan)

4. Charm School by E Watasin

5. Suspended in Language (about Niels Bohr and quantum mechanics by Jim Ottaviani

6. I love so many!  All the illustrated operas by P. Craig Russell, Finder, Grrl Scouts, Black Orchid, Spooked, Lucifer, Concrete: Think Like a Mountain, Courtney Crumrin, Ojo, Hellboy, Finals...  I could go on and on :P