Internet service provider BiGlobe posted two different poll where fans were asked on what anime series fans would most like to see a sequel of.

First survey that was conducted last February 17 and 24  asked fans to what anime series they want to see continued.

Here are the result from 3,935 respondents.

Rankings

1     Toradora!
2     Angel Beats!
3     Tiger & Bunny
4     Castle in the Sky
5     Slam Dunk
6     Oreimo (True Route)
7     Steins;Gate
8     K-ON! (movie)
9     Hanasaku Iroha
10     Highschool of the Dead
11     Arakawa Under the Bridge
12     Yū Yū Hakusho
13     School Days
14     Fruits Basket
15     Katekyo Hitman Reborn!
16     Yosuga no Sora
16     Ōkami-san & Her Seven Companions
18     Blue Exorcist
19     Dragon Ball
20     B Gata H Kei – Yamada’s First Time

Second survey that was conducted last February 20-27 asked fans on anime series , including those with two or more seasons and even film adaptations, they would like to see a sequel to.

Here are the rankings based on 1,842 respondents.

Rankings

1     Angel Beats!
2     The Melancholy of Haruhi Suzumiya
3     Working!!
4     Natsume’s Book of Friends
5     K-ON!!
6     Clannad / Clannad After Story
7     Full Metal Panic! The Second Raid
8     Squid Girl
9     Minami-ke: Betsubara
10     Zan Sayonara Zetsubō Sensei
11     The World God Only Knows
12     My Ordinary Life
13     Bunny Drop
14     Sekirei
15     Rozen Maiden: Ouvertüre
16     Genshiken 2
17     Initial D: Fourth Stage
18     Toradora!
19     KenIchi the Mightiest Disciple
20     Ōkami-san & Her Seven Companions

Anime series that is common on both surveys were Angel Beats, K-ON!, Toradora and Ōkami-san & Her Seven Companions.

[Source]