I have read a few good yuri manga like:
Girl Friends
Kimi Koi Limit
Octave
Blue Friend
Renai Idenshi XX

I'm looking for something which has good romance and has mature/hentai moments in it. Preferably not a collection of stories but rather a single good one even if its a little short ( but not a one shot).
Thanks

I'd say....

Arcadia ~Flowers of Paradise~
http://dynasty-scans.com/series/arcadia_flowers_of_paradise

Prism (it's cancelled... but ended on a good moment to be cut off, sorta)
http://dynasty-scans.com/series/prism

Cirque Arachne
http://dynasty-scans.com/series/cirque_arachne

Spring, Summer, Fall, Winter (theres like 2 stories here, 1 tells the main story, the other is a sidestory, both a few chapters long)
http://dynasty-scans.com/anthologies/spring_summer_fall_winter

Shoujo Holic
http://dynasty-scans.com/series/shoujo_holic

Don't forget Hanjuku Joshi.

http://dynasty-scans.com/series/hanjuku_joshi

Kase-san and The Flower And The Star are the best recommendations for starters i can give, they're both fun, cute and has the best facial expressions you'll ever lay eyes on, especially Kase-san (They're not exactly on the mature side though)

http://dynasty-scans.com/chapters/kase_san_ch01#3

http://dynasty-scans.com/chapters/the_flower_and_the_star_ch01

last edited at Mar 21, 2014 12:39AM

Go through my lists and also look for other works by those authors as well.