According to Dengeki G's Magazine July issue, Key's new project "Angel Beats!" was confirmed to be a TV anime series. It's a collaboration work of Key, Aniplex and Dengeki G's Magazine.

Angel Beats! official website

Staff
Original Scenario & Series Organizer: Maeda Jun
Original Character Design: Na-Ga (Game "Little Busters!")

Synopsis
The story takes place in a world after death. Angels are fighting for the concluded fate and future.
Yuri (nickname: Yurippe, character design) is the leader of "Shinda Sekai Sensen (SSS, World after death Front) and rebels against the god, who destined her to have an unreasonable life. Tenshi (Angel, character design) is the chairperson of the student council of the world after death and battles against SSS members.
SSS members are armed with guns (Yurippe uses M92F BRIGADIER) and the angles use supernatural power.

Source: Scan of Dengeki G's Magazine cover

Update
In a web radio program of Angel Beats!, Maeda Jun said the anime is 13 episode series.

Source: Satsubatsu Radio

Updated on September 28th
Staff
Director: Kishi Seiji
General Graphic Director & Animation Character Design: Hirata Yuzo ("Strike Witches")
Production Studio: P.A. Works

Source: Scan of G's magazine