Here's a list of manga that I personally think you SHOULD be reading. Three out of four are up online, and I know not all of them will be to your liking, but I feel the need to pimp these out because if I don't... who will?

After School Nightmare
Autor
Setona Mizushiro
Length
Ten Volumes – Finished
Why Do I Have To Read This?
Some stories like to fuck with your mind, and Setona Mizushiro is the Queen of Mind Fucking. Every chapter will keep you guessing and each twist and turn will have you starting it over again from the start. Part horror story, part romance, with some action scenes thrown in, After School Nightmare is a beautiful manga.
Where to Buy/Read
Chances are you can find a few volumes hanging out in the manga section of your local book store. However, if the manga section is a bit ‘thin’ you’ll easily get frustrated trying to find it, but there’s always the option of buying it online.

Strobe Edge
Autor
Io Sakisaka
Length
Six Volumes – Japan, so far
Why Do I Have To Read This?
Strobe Edge takes the pain away from most of your typical shojo woes. The pace is quicker than most, and the characters are actually likeable, reasonable, and act like actual human beings. I know, shocking! Yet again, the visuals are eye-bleeding worthy and sometimes the facial expressions are so life-like it tugs at your heart strings to see them upset or happy.
Where to Buy/Read
Read it over on onemanga.com, the first eleven chapters are up.

Karneval
Autor
Mikanagi Touya
Length
Three Volumes – Japan, so far
Why Do I Have To Read This?
A crazy cast of characters, an almost unfollowable plot, but so endearing you can’t help but love the whole experience. Drama, action and hilarity ensues. If you can break into this manga, and I’ll admit it’s not that easy, you’ll be sucked into the world Karneval paints so quickly you won’t have time to be confused. And as always, superb art.
Where to Buy/Read
Read it over on onemanga.com, the first thirteen chapters are up.

Livingstone
Autor
Maekawa Tomohiro & Kataoka Jinsei
Length
Unknown
Why Do I Have To Read This?
Paranormal and dark themes run wild throughout Livingstone. This manga is fairly new and just getting off the ground, so for now all I can say is that the characters are intriguing and the plot seems to be set up pretty well. For those of you wary, Kataoka Jinsei was the artist over on the Eureka Seven manga adaptation, so obviously good taste and great art is involved.
Where to Buy/Read
Read it over on onemanga.com, the first four chapters are up.

I just realized I didn't really put a summary on ANY of these... but feel free to ask/bug me for one if you want one. Or, you know, you could just wikipedia it or click on the convenient links.