Thus, the most memorable anime songs from 2009 for me are:
PAPERMOON by Tommy heavenly6 (Soul Eater OP 2)
Really catchy and fun to sing. The song I listened to the most near the beginning of the year. Also brings up memories of driving school because an instructor asked me to sing a song for extra credit and this is the first one that came to mind. ><;;
Again by YUI (Fullmetal Alchemist: Brotherhood OP 1)
This has pretty much become one of my top favorite FMA songs. It practically defines the series for me. So naturally, I've been listening to it constantly for over half the year.
Namida no Tane, Egao no Hana by Shouko Nakagawa (Lagann-hen theme song)
SIMON/NIA SONG. It made me cry the first time I listened to it, it made me cry after reading spoilers for the movie, and it's another one I've been listening to constantly for over half the year. Can't wait to see it with the ending credit animation. ;__;
LET IT OUT by Miho Fukuhara (Fullmetal Alchemist: Brotherhood ED 2)
I admit I wasn't very impressed with this song when I first heard it. But it grew on me after a while, and with how effectively it was used in the show so many times, I really came to love it.
Melody by Shion Tsuji (Tokyo Magnitude 8.0 ED)
This song will always remind me of summer now. And with how certain episodes of this show made me cry, I still get a little teary-eyed listening to it sometimes.
Tsukiakari no Michishirube by Stereopony (Darker than BLACK: Ryuusei no Gemini OP)
Likewise, this song will always remind me of winter. It seems a lot of people didn't like this OP, but I loved it. Soooo catchy. Also, wow, it seems I watched mostly BONES shows this year. O_o Overall I still have mixed feelings about the second season (I'm waiting for the OVAs to answer some questions), but the music was great nonetheless.
Beautiful World (PLANiTb Acoustica Mix) by Hikaru Utada (Rebuild of Evangelion 2.0 theme song)
I started listening to this pretty late in the year since I only watched the movie via camrip a while ago. But hearing it over the ending credits really struck a cord with me. There's just something about this remix that really feels theatrical and fits the movie perfectly; whereas the original mix of the song from the first movie did nothing for me. Anyway, I've been listening to it constantly for the past month so I still consider it memorable enough to make my list.
Special Mention: "Tomare!" from The Melancholy of Haruhi Suzumiya Season 2, for inspiring RAGE at the end of many an Endless Eight episode. However, I didn't listen to it on its own much.
And that's it for 2009. Happy New Year, everybody!