Tgif! I'm so glad it's Friday!! ^__^ This post will be a list of yuri anime and manga featuring adult characters/storylines. This isn't a definitive list, but it's a good starting point for anybody looking for yuri anime and manga featuring or including adult women:
(the first two titles are available on R1 DVD)
The Devil Lady: the protagonist and three other adult women in the story are canon yuri characters.
Mai Otome (released as My Otome in the U.S.): The sci-fi alternate world spin-off of Mai-Hime, featuring several canon (and heavily implied) yuri characters, both teenage and adult. (Shizuru/Headmistress Natsuki ftw!!)
Blue Drop: There is a subplot featuring a woman (technically an alien woman) seeking to avenge her girlfriend's death.
Available in English:
Pretty much everything by ALC Publishing, like Rica'tte Kanji!? by Rica Takashima, the Yuri Monogatari anthologies by various artisits, and Works by Eriko Tadeno. Yuri Monogatari 6 was recently published, and I'm looking forward to reading it once I go home in May. (I didn't have it shipped to my college address because I already have a ton of stuff to bring home, @_@;; but I'm looking forward to it.) Later edit: Whoops. It looks like I had YM6 sent to my college address when I pre-ordered it. At this point, I don't have time to properly review it until the semester ends, though. -_-;;
12 Days by June Kim, which is about a woman living in New York who copes in an unusual way with the death of her girlfriend while reflecting on their past relationship.
S.S. Astro by Negi Banno, which is a 4-koma comedy about four high school teachers, one of whom is a canon yuri character.
Only available in Japanese (titles that are currently being scanlated or are already scanlated will have an * next to them; titles that will be scanlated by a scanlation group in the future are marked by a +; if you enjoy any of these titles via scanlation, you should support the artist who made them by buying them so that he or she can continue to produce good yuri):
*The Conditions for Paradise by Akiko Morishima: features a three chapter romance between an office worker and her long time best friend who works as a traveling freelance writer, as well as stories about other adult yuri couples.
* Azure Dream by Akiko Morishima: another yuri collection by Morishima featuring numerous adult characters. "Honey Mustard" is especially nice.
*Hanjuku Joshi by Morishima Akiko: focuses on romance between two students at an all-girl's high school, but includes one adult yuri character who works as a teacher (although as a caveat, she does become involved with one of her students).
Any yuri by Yamaji Ebine, like *Free Soul, *Love My Life, *Indigo Blue, and +Sweet Lovin' Baby. I've only read the first two listed, but they are extremely good, mature slice-of-life narratives, and I've heard good things about the latter two.
*Octave by Haru Akiyama: about a woman who was once an idol when she was a teen, but winds up working as a talent manager in Tokyo as an adult, unsure of what she wants to do with her life. Her romance with another former idol, who is now working as a song composer, helps her to reevaluate her life.
*Your Cuteness by Otsu Hiyori: Includes a one-shot titled "Maple Love" about two women in college.
+Clover by Otsu Hiyori: a series of yuri one-shots about four sisters and their respective relationships. The epilogue, taking place three years after the previous chapters, centers around one of the sisters when one them is in law school, living with her girlfriend. I haven't actually read the entire volume yet, but it's gotten very good reviews and I've enjoyed other one-shots by the same mangaka. ^^;;
*Otome-iro Stay Tune by Miyabi Fujieda: chiefly focuses on romance between two seiyuu who voice characters in a yuri radio drama, with a few other adult yuri characters thrown into the mix.
*Chatting at the Amber Teahouse by Miyabi Fujieda: about a romance between the owner of a teahouse and a third-year (or "senior" in the U.S.) high school student who works at the cafe to be near her. In one chapter, an elderly lesbian couple also gives the teahouse owner romance advice.
*Iono-sama Fanatics by Miyabi Fujieda: about the queen of a small, fictitious country who especially loves women with black hair and travels to Japan to find new sobame (ladies-in-waiting). The main character, a woman named Eto, unwittingly decides to become a sobame and falls in love with Iono. The first volume was published in English by Infinity Studios, but they never published the second volume... ;_;
*The Miko's Words and the Witch's Incantations (Kotonoha no Miko to Kotodama no Majyo to) by Miyabi Fujieda: about a witch who frees a miko from the shrine that she was entrapped in as a child and shows her the outside world. (And of course they fall in love. ^^ The miko's protective female bodyguard has a thing for her too.)
*Honey & Honey by Sachiko Takeuchi: a manga that was primarily written to explain lesbian relationships to a straight female audience, following the lives of Sachiko and her girlfriend Masako, along with other people in their lives. An interview with Sachiko Takeuchi can be found here at Tokyo Wrestling, a Japanese lesbian media site (like a Japanese Afterellen) that translates its articles into English and French.
*Plica by Sae Amamiya: a series of webcomics about the daily life of Plica, a young woman in the workforce, her girlfriend Mari, and a few other yuri characters.
*Strawberry Shake Sweet by Shizuru Hayashiya: the protagonists are a high school aged idol and high school aged model, but several of the other characters are adult yuri characters, including the owner of a salon that the main characters frequent and an all-lesbian visual kei group called Zlay (the name is a parody of the real visual kei group Glay).
*Spring Summer Fall Winter by Zaou Taishi and Eiki Eiki: three chapters of this volume are dedicated to the romance between a school nurse and teacher who work at the same school; during other parts of the volume, the school nurse gives romance advice to one of the students.
*No More Need For Chains (Kusari wa Mou Iranai) by Uso Kurata: a Yuri Hime S (*gasp*) one-shot about an office romance.
*Franken Fran by Katsuhisa Kigitsu, chapter 22: This particular chapter of this wonderfully quirky horror-comedy covers a highly unusual yuri romance.
+Papaya Gundan by Aoki Mitsue: about a group of people/friends who work at and run a hostess club. Two of the hostesses fall in love with one another. I haven't read this one yet, but I'm looking forward to reading it since the reviews have been really good.
+Gunjou by Nakamura Ching: about a miserably married straight woman who asks the lesbian woman who is in love with her to kill her abusive husband, and they subsequently go on the lam. Yuri and introspection ensue. I haven't read this one yet, and the plot doesn't sound like my cup of tea personally, but it has received stellar reviews on Okazu and positive reviews in Japan as well.
And although virtually all of the yuri characters in Takako Shimura's Aoi Hana manga are in high school (aside from the protagonist's cousin), the characters are exceptionally mature, while still being realistic teenagers. Hopefully the anime adaptation premiering this July will retain that aspect.