My favorites:
Aqua (Himawari)
Kohaku (Tsukihime)
Kozakai Aya (Hatsuyuki Sakura)
L (Death Note)
Mercurius (Dies Irae)
Others I loved:
Amagi Kojirou (Eve -burst error-)
Archer (FSN)
Asakura ‘Bachelor’ Hikaru (BALDR FORCE)
C.C. (Code Geass)
Hayama Akito (Kodomo no Omocha)
Isono Sepia (Sharin no Kuni)
Kawahara Chisato (X-Change 2)
Kazuo Yoshii (Texhnolyze)
Kino (Kino no Tabi)
Kuki Youkou (Ayakashibito)
Minakami Yuki (Subarashiki Hibi)
Miulu Tiwazu Ar Tonelico (Ar Tonelico II)
Tachibana Kimika (Subarashiki Hibi)
Usami Haru (G-Senjyou no Maou)
Others I liked:
Adachi Toru (Persona 4)
Akagi (Akagi)
Bernkastel (Umineko)
Chloe Hartog (Mana Khemia 2)
Drosselmeyer (Princess Tutu)
Gin (Mushishi)
Gyi (Sekien no Inganock)
Jade Curtiss (Tales of Abyss)
Killua Zaoldyeck (Hunter x Hunter)
Kurogaiya Yuiko (Little Busters!)
Lain (Serial Experiments Lain)
Legato Bluesummers (Trigun)
Misono Sinobu (Virgin Roster)
Morrigan (Dragon Age: Origins)
Nagisa Kaworu (Neon Genesis Evangelion)
Nishijyou Takumi (Chaos;Head)
Ootori Kakeru (Ore-tachi ni Tsubasa ha nai)
Ootori Kanae (Muramasa)
Shin (MinDeaD BlooD)
Shirogane Naoto (Persona 4)
Soma (Ar Tonelico III)
Suwa Mamoru (Chaos;Head)
Tokuchi Toa (One Outs)
Tsuki (Akatsuki no Goei)
Watarai Asuka (Ore-tachi ni Tsubasa ha nai)
Yang Wen-Li (Legend of Galactic Heroes)
Yatouji Satsuki (X TV)
Visual novel & other stuff impressions 