The Oricon Style, a Japanese company responsible for charts of media stuff, made recently a chart which envolves manga supporting characters, whose people would like to see in a spin-off series. Here is the list:
-Through geral:
1# L (Death Note)
2# Char Aznable (Mobile Suit Gundam)
3# Kaede Rukawa (Slam Dunk)
4# Roronoa Zoro
5# Fujiko Mine (Lupin the 3rd)
6# Kuririn (Dragon Ball)
7# Goemon Ishikawa (Lupin the 3rd)
8# Masumi Okuyama (Nodame Cantabile)
9# Shinchi Okazaki (Nana)
10# Usopp
-Through female public:
1# L (Death Note)
2# Kaede Rukawa (Slam Dunk)
3# Masumi Okuyama (Nodame Cantabile)
4#Reira Serizawa (Nana)
6#Rui Hanazawa (Hana Yori Dongo)
7# Fujiko Mine (Lupin the 3rd)
8# Goemon Ishikawa (Lupin the 3rd)
9# Ryutaro Mine (Codename Cantabile)
10# Roronoa Zoro
-Through male public:
1# Char Aznable (Mobile Suit Gundam)
2# L (Death Note)
3# Kuririn (Dragon Ball)
4# Roronoa Zoro
5# Usopp
6# Colonel Roy Mustang (Fullmetal Alchemist)
7# Fujiko Mine (Lupin the 3rd)
8# Inspector Zenigata (Lupin the 3rd)
9# Daisuke Jigen (Lupin the 3rd)
10# Sumire Onda (Bayside Shakedown)
Source: NeoTokyo (Brazilian magazine)