Directly from the Announcement sections on the forums, as of today:

Regarding Character Creation Restrictions (Sep. 1): Follow-up 5
Currently, we have stopped allowing the creation of new characters in the following Worlds:

Adamantoise
Aegis
Anima
Atomos
Bahamut
Balmung
Behemoth
Cactuar
Carbuncle
Cerberus
Chocobo
Diabolos
Durandal
Excalibur
Exodus
Gilgamesh
Goblin
Gungnir
Hades
Hyperion
Ixion
Kujata
Leviathan
Malboro
Mandragora
Masamune
Midgardsormr
Moogle
Odin
Phoenix
Ragnarok
Ridill
Sargatanas
Shiva
Siren
Tonberry
Typhon
Ultima
Ultros
Valefor
I think they're pretty much all up on that list. If you find one that isn't, that's where you have your best chances. But overall, just acknowledge the fact that the current server capacity in general is simply being overwhelmed, and there is probably no server that isn't suffering from login restrictions at some point. They are adding more servers this coming week, we're not really sure yet if or how this will affect the populations / availability of the existing worlds though, but let's hope they figure something out.