Here's a list of my top 10 yuri anime of 2009, followed by a list of my top 10 yuri anime of the past decade.
My Top 10 of 2009:
Honorable mention goes to Shin Koihime Musou (for the sheer number of yuri characters) and Kanamemo (for Yume and Yuuki, even if Haruka...well, everybody who reads this blog already knows how I feel about Haruka).
My Top 10 of the Past Decade:
8) Mai-Hime- For being a popular action title that gave rise to a popular yuri couple, among numerous other potential pairs. It spawned even more yuri in its spin-off, Mai-Otome, and in the two OVAs that branched from Mai-Otome. Not to mention Mai-Hime Destiny, Mao-Hime (I think that's what it's called...I haven't really bothered with reading it), and the upcoming Mai-Hime EXA. (I'm trying to forget the first Mai-Hime manga.)
2) Aoi Hana- Simultaneously the best and most realistic title centered around a canon yuri protagonist in the past decade.
1) Maria-sama ga Miteru: Because no other yuri title that aired from 2000 through 2009 has been as influential or as heavily-referenced as Marimite.
And that's it. ^^ Whatever you agree or disagree with, hopefully you got something (entertainment? befuddlement? irritation?) out of it. I took into account: A) what I liked, B) what was good (which is still subjective), C) what was influential, and D) what marked noteworthy shifts/trends in yuri anime. (The latter two factors aren't immune to subjectivity either, of course.)