The site also doesn't actually specify that it needs to be a Japanese seiyuu, but I'm guessing that's what they're going for. So I thought I'd throw out the names of some of the busiest seiyuu in 2009.
- Daisuke Namikawa (07-Ghost's Mikage, Hanasakeru Sheishounen's Rumaty, Hetalias North Italy and South Italy, Kimi ni Todoke's Shota Kazehaya
- Daisuke Ono (11eyes' Kakeru, Hanasakeru Seishounen's Eugene, The Melancholy of Haruhi Suzumiya Second Season's Itsuki Koizumi, Minamike: Okaeri's Hosaka, Pandora Hearts' Jack, Sora Kake Girl's Shigure, Munto's titular Munto, Umineko no Naku Koro ni's Battler.
- Jun Fukuyama (Akikan!'s Kakeru, Viper's Creed's Haruki, Sora Kake Girl's Leopard, Valkyria Chronicles' Maximillian, Spice and Wolf II's Kraft Lawrence, Pandora Hearts' Vincent Nightray, 07-Ghost's Hakuren, Tegami Bachi's Gauche Suede, Saki's Kyoutarou Suga, Shangri-La's Sion Imaki)
- Mamiko Noto (Maria-sama ga Miteru 4th's Shimako Toudou, Nogizaka Haruka no Himitsu's Haruka Nogizaka, Kimi ni Todoke's Sawako)
- Hiroshi Kamiya (Zoku Natsume Yuujin Chou's Takashi, One Piece's Trafalgar Law, Bakemonogatari's Koyomi Araragi, Zan Sayonara Zetsubou Sensei's Nozomu Itoshiki)
- Miyuki Sawashiro (CANAAN's Canaan, Tegami Bachi's Lag Seeing, Phantom: Requiem for the Phantom's Drei)
- Maaya Sakamoto (Kuroshitsuji's Ciel Phantomhive, Soul Eater's Crona, CANAAN's Alphard)
- Aya Hirano (Fairy Tail's Lucy, Kiddy Girl-and's Lumiere, Queen's Blade's Nanael, The Melancholy of Haruhi Suzumiya Second Season's Haruhi Suzumiya, White Album's Yuki Morikawa)
- Rie Kugimiya (Fairy Tail's Happy, Basquash!'s Flora Skybloom, Fullmetal Alchemist: Brotherhood's Alphonse Elric, Hayate the Combat Butler!!'s Nagi Sanzenin, Kanamemo's Mika Kujiin, Maria-sama ga Miteru 4th's Toko Matsudaira, Saki's Yuuki Kataoka, Shakugan no Shana S's Shana)
- Romi Paku (Bleach's Hitsugaya, Fullmetal Alchemist: Brotherhood's Ed Elric, Hetalia's Switzerland, RideBack' Tamayo Kataoka, Spice and Wolf II's Abe)
- Yui Horie (Bakemonogatari's Tsubasa Hanekawa, Tower of Druaga's Fatina, Umineko no Naku Koro ni's Maria, Kampfer's Akane, Saki's Mihoko Fukuji)
- Nana Mizuki (White Album's Rina Ogata, RideBack's Rin Ogata, Darker than Black: Ryuusei no Gemini's Misaki Kihara, Shugo Chara!! Doki's Utau Hoshina)
- Minori Chihara (Minamike Okaeri's Chiaki Minami, Saki's Touka Ryuumonbuchi, Tower of Druaga's Coopa, The Melancholy of Haruhi Suzumiya Second Season's Yuki)
- Yuuko Gotou (Tears to Tiara's Rhiannon, Queen's Blade's Menace, Zan Sayonara Zetsubou Sensei's Abiru Kobushi, The Melancholy of Haruhi Suzumiya Second Season's Mikuru)
- Marina Inoue (Minamike: Okaeri's Kana Minami, Maria Holic's Matsurika, Umineko no Naku Koro ni's Jessica, Valkyria Chronicles' Alicia, Kampfer's Natsuru)
Of course, prolificness isn't necessarily the sign of a good seiyuu-- there was just no way I could list every seiyuu who had a lead this year, much less every seiyuu who had a role! Will you submit a nomination? If so, who will it be?
Personally, I think I'm going to submit Marina Inoue-- I think for sheer versatility of roles, she's done an amazing job.