You guys forgot 'Now and Then, Here and There'. I believe it and 'Grave of Fireflys' pretty well define dark anime.
 
Blood the last vampire-
Vampire hunter D
Vampire hunter D- Bloodlust  ( these two are together )
 
Demon City Shinjuku
3X3 Eyes
 
Boogiepop Phantom
SciFi Harry 
Try those and I'm sure Perfect Blue has been metioned as well.
 
Jin-Roh
very dark and sad!
 
 
even my Dad (who doesnt like Anime) 
was touched by it!
chris
 
 
Witch Hunter Robin
Wolfs Rain
 
nicechris Wrote:Jin-Roh
very dark and sad!
 
 
even my Dad (who doesnt like Anime) 
was touched by it!
chris
Than I should watch it..Bought it but its just collected dust
 
 
These are all the ones at the moment.Hope it helps.^_^
Vampire Princess Miyu ovas
12 Kokuki 
NaruTaru
Raxhephon
Key, the metal idol
Saikano
Blue Gender
Witch Hunter Robon
Texnolyze
Grave of the fireflies
A dog of flanders
X-TX
Shingetsutan Tsukihime
Now and Then, Here and There
Hoshi no Koe
Millennium Actress 
Wolf's Rain
Chrno Crusade
Gunslinger Girl
Kiddy Grade
.hack//SIGN
Monster 
Ayashi no Ceres
Bleach
Rurouni Kenshin ovas
 
try project ARMs or vampire hunter D/bloodlust
 
I would go with Gungrave or Blue Gender.  I have also heard that Evangelion is dark.