Oh, hm--I thought you would enjoy Ahiru, she's a nice girl. Have you seen Zetsubou-Sensei? I don't think it's been licensed, but you might like it. Haibane Renmei has some cute shoujo ai elements.
(Unfortunately, I don't think I've read or seen anything out of doujinshi that was actual yuri)
How about Welcome to the NHK, by the way? Anyone... ? I keep on thinking about this one and forgetting about it.
I watched Sayonara Zetsubo Sensei via fansubs and found myself experiencing mixed feelings while watching it. Personally the part of it I liked and found memorable was the opening theme song, which is one I am kind of partial to if not fond of. Outside of that it's not one I would want to own.
Now I looked up some reviews and articles on both Princess Tutu and Haibane Renmei. Princess Tutu doesn't sound like an anime I would enjoy. I'm not big on magical girl anime and when it comes to anime I'd rather have something josei than shoujo any day of the week as experienced by my enjoyment of Honey and Clover and Usagi Drop. However I'm more interested in seinen anime and only enjoy josei anime on occasion.
As for Haibane Renmei I'm kind of experiencing mixed feelings on wanting to watch it and worrying that if I watch it I'm going to be about as confused and disturbed as when I watched another one of Yoshitoshi ABe's other works, Serial Experiments Lain. You can put me down for that one as me perhaps watching it when I'm in the right kind of mood for it.
Speaking of that however I actually want to watch Welcome to the NHK, which is also by Yoshitoshi ABe and on Amazon.com is available for under $20. It's one of the anime I had in mind when I started thinking about maybe making a purchase of some kind, the others being Kashimashi: Girl Meets Girl and Strawberry Panic.
Now Kashimashi: Girl Meets Girl is a nice little yuri anime that while being made with a male audience in mind is in my opinion beautiful, heartfelt and tasteful. I've seen it before and quite personally I think it's pretty good. If you want a little synopsis about what said anime is about...
Hazumu is a mild-mannered boy who likes gardening and gets picked on because he's kind of effeminate. He has a crush on his close friend Yasuna and he confesses one day only to be rejected by her. He decides to go to the mountains near town to commune with nature and cheer himself up when all of a sudden an alien spaceship crashes into the mountainside and in particular where Hazumu is standing.
His tomboy childhood friend Tomari as well as Yasuna see the spaceship crash and go up there to check and see if Hazumu is okay, only to find out that the alien in the spaceship which destroyed Hazumu's body has reconstructed him while making the mistake of giving him a sex change at the molecular DNA level, thus bringing Hazumu back to life as a female. This leads to an interesting situation where now both Yasuna and Tomari are interested in Hazumu, the alien and the spaceship's AI decide to move in with Hazumu to study her, and Hazumu's best guy friend Asuta is confused as all hell and liking it.
Strawberry Panic on the other hand is a yuri anime based off of a series of light novels that I only know of because a 4chan /gif/ video set to the tune of "Bat Country" by Avenged Sevenfold featured a clip from it that I thought was funny. I'm thinking of getting it largely because the plot sounds interesting and because the clip kind of sold me on the anime itself.