What do you think about this list?
Undead Burg ( 5 10 )
Undead Parish ( 10 20 )
Lower Undead Burg ( 20 30 )
The Depths ( 20 30 )
Blighttown ( 30 40 )
Quelaags Domain ( 35+ )
(Second bell of awakening generally rung around lvl 35)
The Catacombs ( 30 50 )
The Great Hollow ( 45-55 )
Ash Lake ( 45-55 )
Darkroot Garden ( 35-50 )
Darkroot Basin ( 35-50 )
Valley of Drakes ( 40 60 )
Undead Asylum Revisited ( 30 40 )
Sens Fortress ( 35-45 )
Anor Londo ( 45-60 )
Painted World of Ariamis ( 60+ )
New Londo Ruins ( 60+ )
The Abyss ( 50 70 )
The Dukes Archives ( 50-70 )
Crystal Cave ( 55-75 )
Tomb of the Giants ( 55-75 )
Demon Ruins ( 60-75 )
Lost Izalith ( 65-80 )
Kiln of the First Flame ( 70 100 + )
http://daydull.com/tips-tutorials/dark-souls-recommend-levels-for-areas-and-bosses/
I'm also wondering about the DLC areas.