Well there aren't really that many ecchi yuri animes so far i know, and i like the yuri animes too...
But i will just list some that might fit into that genre.
Candy Boy
Yukino and Kanade Sakurai live together as high school students enjoying their daily life; until one day Sakuya Kamiyama confess her love for Kanade to Yukino, asking for her support. This makes Yukino to release her true feelings for her sister.
Kannazuki no Miko
The highborn Himemiya Chikane is cool and aloof, the perfect young lady of good breeding. Kurusegawa Himeko is devoted to her, and secretly her friend.
Kashimashi ~Girl meets Girl~
Hazumu was a shy boy who enjoyed gardening, collecting herbs, and long walks in the mountains. One day he finally worked up the courage to confess his love to Yasuna, but she rejected him.
Yami to Boushi to Hon no Tabibito
Maria+Holic
A sophomore named Kanako who enrolls in all-girls school because she has a phobia of men and wants to find her destined yuri partner. She meets a captivating freshman named Mariya who fits her criteria—except her seemingly ideal mate happens to be a cross-dressing sadistic boy.
Sasameki Koto
Sumika Murasame is deeply in love with her cheerful classmate and friend Ushio Kazama. Ushio is openly lesbian but... she likes cute girls, and Sumika, top student, class representative, black belt in karate, is all but cute. Even worse, Sumika herself is terrified of endangering her friendship with Ushio and chooses to maintain the status quo, as much as it pains her to hide her feelings...
Strawberry Panic
Aoi Nagisa transfers to a new Catholic girls only school and discovers a community of fellow students entwined in an intricate heirarchy, at the top of which sits the all important Etoile. In order to fit in, Nagisa must go to class, join clubs, and make new friends. Meanwhile, Shizuna Hanazono, the Etoile of the school, finds herself drawn to this new, exciting transfer student. As Shizuna and Nagisa get to know eachother, Shizuna finally decides it is time to face her troubled past.
Aoi Hana
Fumi Manjoume, an introverted, bookish teenage girl, is beginning her first year of high school at Matsuoka Girls' High School. She enters the school year with her heart broken by a previous relationship. At about the same time, she reconnects with her best friend from ten years ago, Akira Okudaira, who is now attending Fujigatani Girls' Academy as a first-year high school student. As they reconnect, they both deal with their own respective romantic problems, and help each other get through them.
Kämpfer
Senō Natsuru is your normal, everyday high school student. However, he's been chosen to be a Kämpfer, who's objective consists on fighting other Kämpfer with either guns, swords or magic. However, there's catch—first, you can't chose if you're a Kämpfer or not, and second, you must have the body of a girl to use your powers.
Kuttsukiboshi
Mnemosyne
Rin Asōgi may look like an ordinary office lady on the outside but she is actually a private investigator taking on any jobs, from finding a stray cat to infiltrating a high-security corporate lab. What's more, she appears literally indestructible, supernaturally healing any injuries and mutilations. Together with her partner Mimi, Rin delves into the darkest secrets of the society but the ones she hides herself are by far more sinister...
Shoujo Sect (Hentai but it's good)
Shinobu Handa and Momoko Naitō have known each other since childhood. Shinobu fell in love with Momoko the first day they met. Now in high school, Momoko has forgotten about the past, but Shinobu hasn't. Both follow their own ways but Shinbobu still hopes for Momoko to remember their promise from long ago.
Sono Hanabira ni Kuchizuke wo – Anata to Koibito Tsunagi (Hentai too)'
Is the story of two girls, Miu and Reo. One day Reo grabs a cold, so Miu stays to take care of her. Through out the OAV, their relationship develops into a wonderful love story.
Strike Witches
That's all i can remember so far, but there are a lot more without the ecchi genre, for instance just yuri hints or just normal yuri without ecchi but i hope it was any help.
Would like to mention all i know so far ! :D (anwer was too long with a summary ! :D)