Mahou Sensei Negima!, the manga from Akamatsu Ken, author of Love Hina,
features a class of 31 classmates.

In the latest Shonen Magazine, the seiyuus for all 31 of them are
announced.  Check the list (in Japanese) on the 12/3 entry at Akamatsu's
dairy.

http://www.ailove.net/diaries/diary.cgi

They managed to get quite a few seiyuus who had had major-roles in there.

I didn't find an anime announcement, only a few character CDs are
announced for the moment.  And there will be a debut event on 12/23 that
is free to 900 people who sents in post cards and wins a lucky draw.

Stephen