Recently I read KIMINO Sakurako's Strawberry Panic! and I fell in love with it. It reminded me in a way of another one of my favorite manga, KONNO Oyuki's Maria-sama ga Miteru. I was hoping to find other series that have similar storylines. Can anyone help me out?

Try First Love Sisters

I guess you're looking for school-life shoujo-ai...

Then how about Clover (OTSU Hiyori)? Only a collection of short-stories, but it's still pretty good.
Youkai Gakuenki
Sasameki Koto
Shibuya District, Maruyama Neighborhood: After School - Only a one-shot, though.
Himitsu no Kaidan
Maybe Oniisama e... - but I haven't read it so I can't be certain.

Shiroi Heya no Futari was a pioneer of the "melodramatic all-girl school shoujo ai romance" trope.

Pieta

[img]http://www.nodiatis.com/pub/11.jpg[/img]

Moved to Yaoi/Yuri~

Thank you everyone for your recommendations so far, I really enjoyed First Love Sisters (thank you HiddenSideQuest for that ^^)
and thanks calstine for recommending Clover (OTSU Hiyori), it is really good, I loved it ^^
and one more thanks to Rainy Days for moving this Yaoi/Yuri for me, but I will say this, and I probably should have before, but I am not interested in any of the yaoi stories like this, it's just not the same appeal

Thank you again everyone who replied to my thread. I finally made it through all of your suggestions, and I loved them. Thank you very much Superfreak for suggesting Pieta, it was one of the greatest mangas I have ever read, so thank you. Thank you to Plate as well, for the suggestion of Shiroi Heya no Futari, it was so beautiful, the ending made me cry, so thank you very much.

I had an ulterior motive for replying again, though. I was hoping that someone might have more suggestions for me, because this is a style that I have completely fallen in love with. If anyone can give me any other similar titles, I would greatly appreciate it. Thanks in advance to anyone who can help me. ^__^