Update: Review for this book is up.
Udon has just announced that they will be releasing DISGAEArt!!! Disgaea Official Illustration Collection in August 2012.
It's the English translation for the original Japanese edition 魔界戦記ディスガイア 公式イラストコレクション :DISGAEArt!!!.
The book features art from all four Disgaea games and the art of Takehito Harada. You'll see art for game covers, books, and other promotional and merchandise items.
Below are some preview pages.