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That's a of a tall & wide order. Are there any specific genres you're looking for? Maybe list some of your favorites so we can get a feel for what you like.

I apologize for taking so long to get back. It’s been a busy week. Although, I’m surprise no one else wanted to recommend something.
Side note: (Yes a few of these are above our PG-13 recommendation limit but since the poster say they are 19 I'm going to go with it.)

Upotte, Girls Und Panzer, & Stella Academy Class C3 all have a sort of girls with guns theme working.
So keeping with that maybe you’ll like Strike Witches. A couple of your titles tell me you don’t seem to mind things a little darker so I'm going to go with possibly Gunslinger Girl and its sequel Gunslinger Girl: Il Teatrino because they are shows about preteenish assassins. Black Bullet is a currently airing series that also deals with school girls carrying guns and kicking butt. It might be a medium between GG and the titles you mentioned. It’s serious but silly. I also hear Himawari! is similar to Upotte with the difference of the girls in Himawari! are ninjas.

AKB0048, Pretty Rhythm Aurora Dream, Pretty Rhythm Rainbow Live, & Aikatsu! keep with a pop idol premise.
This is so not my genre but I’m going to try. Did you watch Pretty Rhythm: Dear My Future as well? Senki Zesshou Symphogear: Meteoroid-Falling, Burning, and Disappear, Then... keeps with the space, sci-fi genres of AKB0048 so maybe you'll like it too. Hime Chen! Otogi Chikku Idol Lilpri is magical girl pop idol goodness that might fit your taste. The iDOLM@STER & Love Live! School Idol Project are titles that deal with idols on a more realistic basis. Also, there's a new series coming this summer called Futsuu no Joshikousei ga [Locodol] Yatte Mita., you might want to lookout for it. And perhaps if you'd like to switch to male idols there’s Uta no☆Prince-sama♪ Maji Love 1000% and its sequel.

Death Note
The Future Diary & Monster are both psychological thrillers that fans of Death Note seem to enjoy. Or perhaps even Jigoku Shoujo series. Basically the show is: At midnight go to the site and if you’re lucky type in the name of a person you have a grudge against. They will be sent to hell but, there is a price. Kind of Death Note like right? Personally I like Hell Girl.

Black Butler
Makai Ouji: Devils and Realist, Inu x Boku SS & Pandora Hearts are all stories of rich/aristocrat kids being protected by their respective demon butlers, fox spirits, etc. You may like Gosick because it’s a mystery solving title placed in that sort of older European setting. Earl and Fairy although in my mind isn't quite like BB it also incorporates the themes of "an era gone by" England (although Kelpies are a Scottish myth), aristocrats, supernatural, & deadly butlers.

"Sakura Kiss" as in the song by Chieko Kawabe used in Ouran High School Host Club right? I love her song "Be Your Girl" which was used as the ending to Elfin Lied. Let me get back to you on that one.