Annotations can be copied from http://konachan.com/post/show/268594/
I've converted all the copyrights across. himeno_eien couldn't be linked to a copyright to convert properly.

Hime Cut Black Hair Party

There are a lot of weapons in there.

We need more of these.

I remember there was a pink hair party image too.

That bifurcated blade next to the left-side racks of katanas, isn't that the Di-Sword of aoi sena from Chaos;Head? Does that mean she's somewhere in this picture?

Kurzwaltz said:

That bifurcated blade next to the left-side racks of katanas, isn't that the Di-Sword of aoi sena from Chaos;Head? Does that mean she's somewhere in this picture?

Yes

Now to identify each and every one of these. I only managed to find Shana, Alastor and Kei, as well as Homura's shield.

Kurzwaltz said:

That bifurcated blade next to the left-side racks of katanas, isn't that the Di-Sword of aoi sena from Chaos;Head? Does that mean she's somewhere in this picture?

Not necessarily, look at the artist's commentary. Some of the girls are only represented by items associated with them.

I tried to look for Suoh from Flowers, but without the annotation on Konachan, I sure would have ever guessed who she is. The characters from behind are pretty much impossible to recognize on your own. I did, however, manage to identify Zakuro from Subahibi (and that before I saw the respective tags) and added a note for her. Since I was at it, I copied some more annotations from Konachan, but I don't have the time to do them all right now.

A few IDs (some speculative):

The girl near the middle with red cross-stitching is Sanka Rea, I think.
Below Yomi could be Kanoe Yuuko (aka Ghost Yomi) from Tasogare Otome x Amnesia. Breasts seem a little small to be her though. Nearby, facing away, is Tatsumiya Mana.
At the back, the girl with gray, empty eyes is from Houkago Play. Behind her and to her left, on the coatrack are the outfits of Akiha (Tsukihime) and Kaguya-hime (Touhou). To her right, the labcoat and sweater combo belongs to Yagiri Namie
Akemi Homura's shield is on the wall.
The two part picture at the very top has Koumori Kuroko (with the crazy tongue) and Kitsu Chiri
Ichihara Yuuko is highest on the stairs.
She's not tagged, but girl on the right with arm raised and looking directly at the viewer might be Rory Mercury.

@SciFi:

It appears 姫野永遠 should be read as Himeno Towa, not Himeno Eien.

I have translated the first part of the "guest list", which gives the names of every girl physically present.

The following 12 7 have not yet been identified in the picture:
Akame (Akame ga Kill!)
Amano Tooko (Bungaku Shoujo)
Enma Ai (Jigoku Shoujo)
Kamura Reiri (Kaibutsu Oujo)
Kawakami Momoyo (MajiKoi)
Kujou Sakurako (Sakurako-san no Ashimoto ni wa Shitai ga Umatteiru)
Komachi Tsugumi (Ever 17)
Shionji Yuuko (Kami-sama no Memo-chou)
Shinokawa Shioriko (Biblia Koshodou no Jikentechou)
Nagumo Kasumi (Memories Off Yubikiri no Kioku)
Hayakawa Ryouko (Shibito no Koe wo Kiku ga Yoi)
Yamashina Itsuki (Kimi no Knife) (Hard to find references).

Correspondingly, 12 7 girls in the picture have not been identified:
1 at far left, half off the side; yellow eyes and wearing a yellow dress
1 at left, between Utaha and Fuyumi; dark eyes and drooling
1 at top left, facing away; holding Enoki Sachi's hand Tentatively Hayakawa Ryouko. Both her and Enoki are ghost schoolgirls.
1 a little above center, facing away; with Karyou Kaie and female Alucard. As mentioned, much higher than average chance of being a trap or transgender. Tentatively Kamura Reiri. I seem to recall her have a thing for dressing boys in girls clothing. Also a vampire like Alucard, despite the huge power gap between them.
1 a little right of center, facing away; apparent focus of attention for Yomi and Hazuki Mina. Might be Akame; all three would be swordfighters.
2 behind Hazuki Mina: one is blushing, has arm raised and is clutching a green book. EDIT: The book is The Wonderful Wizard of Oz, and is western-style left to right. Tentatively Amano Tooko, the "Literature Girl". The other is facing away and is touching the former's chin. Konachan seems to think this is Momoyo, but I'm not seeing it.
2 at right, besides Yuuko's raised arm; both appear to be looking at a waraningyou. Tentatively Shionji Yuuko and Enma Ai. Both are substantially shorter than the average here.
2 talking at lower right. The one who's face we can see might be Sakurako, but if so the artist forgot a prominent mole beneath her right eye.
1 at far right side seen in profile, near Ayatsuji Tsukasa. Appears to be wearing a black ribbed sweater.

Someone on Konachan pointed out that Shana, Akiha and Sakurai Kei are/were seated at the same table. All three have hair that turns red when they "get serious".

One of the swords (specifically the one with a red piece of string wrapped around its sheath) belongs to Tendou Kisara from Black Bullet.

EDIT: Second from the left on the photo on top seems to be Himegami Aisa (To Aru Majutsu no Index). The hime cut, outfit, and utterly dead expression seem like a solid connection.

Finding your waifu in this mess is like "where's waldo" on hard mode - every character on the page looks kind of like Waldo. Good fking luck.

What is this, heaven?

When I looked for Mio, I was expecting her to be in a corner either embarassed or scared to be there. I guessed wrong.

There are 41 characters inside and 15 outside. All the outside characters are wearing their most common outfit, whereas those inside have changed. On the clothes rack at the back, there are 37 outfits which are visible in part; assuming hangars are spaced evenly, we can suppose an additional three which are totally obscured.

Starting from #1 on the left and going to #40 on the right:
1. black serafuku with white kerchief, single stripe: Minagami Sakuya
2. unbuttoned white shirt, loose green tie: Shibuya Rin
3. black serafuku with white kerchief, double stripe: Hirasaka Hatsune
4. unidentified. Branch of Hourai is giving off colored light which makes determining actual color difficult
5. unidentified. Something light blue. Collar looks odd.
6. unidentified. Grey, lighter grey lapel outlined in white, white collared shirt.
7. red tuxedo jacket with black lapel: Jabami Yumeko
8. totally obscured by Nagato
9. black at the shoulder with white midsection, brown line on sleeve: Nagato, specifically her Kai-2
10. black serafuku with red kerchief, double stripe: Kamura Reiri
11. black serafuku with red kerchief, single stripe, no center bit to get in the way of good cleavage: Kanoe Yuuko
12. white-on-grey serafuku, black collared shirt, red/pink neckwear: Kuroda Sayuki
13. very MiB; black suit and tie, white shirt: Hazuki Mina (right)
14. two-tone green and teal sweater, dark skirt and white labcoat: Yagiri Namie (the famous Durarara! 1st season ED; third from the bottom)
15. black jacket with red buttonloops: Natsuno Kirihime
16. dark blue shirt with bright blue bow: Kuroyukihime
17. blue chinese dress with red and yellow flower patten: Karyou Kaie
18. pale plue blouse with red ribbon, long red skirt: Toono Akiha
19. pink shirt with many white bows: Houraisan Kaguya
20. black over white collared shirt, blue neckwear: Touma Kazusa
21. unidentified. white/gray over black collared shirt, red neckwear barely visible
22. red neckite, black vest, striped shirt collar: Akame
23. plain white buttoned shirt, cuffed sleeves: Kujou Sakurako
24. white open jacket over black shirt: Kawakami Momoyo (right)
25. blue on white serafuku: Irisu Fuyumi, albeit missing double stripe
26. red on white serafuku: Ajimu Najimi
27. light blue pajamas with bear print: Shionji Yuuko
28. white sleeveless pullover, black skirt: Shinokawa Shioriko
29. light blue on white serafuku, wheat pattern on sailor collar: Amano Tooko
30. completely black, purple ribbon, purple belts: Komachi Tsugumi (right)
31. white on black serafuku, red kerchief: Enma Ai
32. unidentifiable, totally obscured by Hagoromo Gitsune
33. black with gray trim, gray ribbon left of center: Isayama Yomi
34. dark blue-green cable knit sweater, red ribbon: Nagumo Kasumi (external link)
35. black, lapel outlined in white: Yukinoshita Yukino
36. unidentifiable, totally obscured by Hirasaka Hatsune
37. white on blue-gray serafuku, double stripe: Kasumigaoka Utaha
38. black jacket over tan sweater: Ayatsuji Tsukasa
39. unidentified. Mostly obscured by Kanoe Yuuko's arm, what is not is entirely black
40. black, white waistband, collar is appears lacy, orange ribbon: Shirahane Suou

Those without matches:
Alucard (Hellsing: The Dawn)
- white jacket, white buttoned vest, red necktie, white cylindracal hat
Ichihara Yuuko (xxxHolic)
- CLAMP uses so much variety in her wardrobe I'm not sure she has a single characteristic outfit
Kawakami Tomie (Tomie)
- most art emphasizes her creepiness and not her wardrobe. No consistent outfit.
Kurosawa Dia (Love Live! Sunshine!!)
- white or off white on grey serafuku, grey pleated skirt, usu. green neckerchief
Sakurai Kei (Dies Irae)
- either blue on white serafuku with diamond-shaped cutout on left sleeve, or black trenchcoat over white collared shirt, black tie
Shinonome Satsuki (Koi to Senkyo to Chocolate)
- essentially a green virgin killer outfit + green shrug (clothing)
Shana (Shakugan no Shana)
- summer: white on olive serafuku, yellow neckerchief
- winter: all olive, double breasted, grey neckerchief
Semiramis (Fate/Apocrypha)
- very complicated, likely impossible to place on a hangar in the first place
Hagoromo Gitsune (Nurarihyon no Mago)
- all black serafuku, except for white neckerchief

props to the artist this is great

Hime cut heaven ^____^

God is not dead.

it still amazes me how at first glance my brain just sees a bunch of generic black hair characters but we can still tell each individual character

I'm so glad I stumbled across the post. Long, straight, black haired woman supremacy!!