List them anyway, C. There's a chance I may not know a name and a chance that one may have slipped my mind.
Oh wait. Yuri Monogatari 5 has that one story about an elderly woman having sex with the granddaughter of the woman she was in love with. It was meh.
If someone wants to accuse us of eating coconut shells, then that's their business. We know what we're doing. - Achaan Chah@ Aondeug - Okay, let's list some (although not judging them based on quality)
Yuri series where the protagonists are 18-35 but not in an ongoing relationship (not including supernaturally young protagonists):
- Ame-iro Kouchakan Kandan (1/2 initially but both eventually)
- Ebisu-san and Hotei-san
- Haru Natsu Aki Fuyu (Specifically the First Kiss chapters)
- The Mikos Words And The Witches Incantations
Yuri series focusing on an ongoing relationship involving a pair of teenagers:
- Aoi Hana
- First Love Sisters
- Girl Friends
- Gokujou Drops
- Hanjuku Joshi
- Haru Natsu Aki Fuyu
- Kimochi No Katachi
- Morinaga Milk's Nana/Hitomi story
- Otome Senshi Lovely 5
- Sono Hanabira Ni Kuchizuke Wo (Games 1,2,3,4,5,6,8)
Yuri series with adult main characters in an ongoing relationship (ignoring supernaturally young characters):
- Chirality (1/2)
- Honey and Honey
- Iono The Fanatics
- Junsui Adolescence (1/2)
- Maka Maka (Quasi-relationship mind you)
- Octave
- Pieta (Though still in highschool)
- Sono Hanabira Ni Kuchizuke Wo (Games 7 & 10; 1/2)
- Wife And Wife
Edit: Moved Pieta to the third category based on what Miijhal let me know. Game eight of Sono Hanabira Ni Kuchizuke Wo may also belong in the third category because the protagonists could be 18 years old.
edited 27th Mar '11 4:17:19 PM by CBanana
and that's how Equestria was made!@C Banana: The characters in Pieta are both around 20 years old, actually.
edited 27th Mar '11 4:04:32 PM by Miijhal
Ah. Well, strike that one off the list. Thanks.
Also, reading 'Nobara no Mori no Otome-Tachi!'.
...I'd find it hilarious if all the yuri series set in girl's catholic schools resulted in an influx of lesbian and bisexual students in Japanese catholic schools. :P
edited 27th Mar '11 7:00:40 PM by Miijhal

As for ongoing relationships and/or yuri characters who are 18-35, I could recommend some series to Aondeug but I'm certain she already knows about them and just hasn't gotten around to them yet.
and that's how Equestria was made!