Hmmm...
My vote goes for the following:
Shinkirou (Ending song of Black Blood Brothers) by LOVEHOLIC
>> The chorus just kept on creeping back in my head
Broken Wings (Ending song of Trinity Blood) by Tane Tomoko
>> It's so soothing... the music...
Lilium (Opening Song of Elfe Lied) by Kumiko Noma
>> Yeah... I have a pretty weird taste in music... My blockmates who borrows my MP4 and happens to chance upon all three versions of Lilium (original version, saint version and music box version) thinks that it's from a horror film or something... I dunno with them... Anyway... I like the music box versionby Kawabe Chieko best... since itreally sounds so sad... Oh yeah, the saint version is by GRIFFIN CHORUS...
Still Doll (Ending song of Vampire Knight) by Kanon Wakeshima
>> Although the anime version is nothing compared to the manga, the ending song by Kanon Wakeshima (produced by Mana of Malice Mizer) had somehow captivated me... *groan* how I wish I have a cello...
Karenai Hana (Ending song of Full Metal Panic)
>> I love singing these kinds of songs... Well, since they're really easy... Yet interesting...
Now for the loud ones.... I love the following:
Hey! Billy and What's Up People by Maximum the Hormone
>> Naturally I have a lot of otehr songs in my head... but these may be my top ones...