And the first available Disgaea 4 DLC is...

[burnfist23.livejournal.com]

http://www.andriasang.com/e/blog/2011/03/24/disgaea_4_toro_kuro/
http://news.dengeki.com/elem/000/000/355/355009/

Well, at least they're getting them out of the way.

UPDATE: Here's the Toro and Kuro cut scene:
http://www.nicovideo.jp/watch/sm14017356

The official site is conducting a DLC poll though NI has a history of not sticking to the poll.

http://disgaea.jp/4/news/vote.html

You can vote for anyone, I think, but the suggestions they have listed are:
Marona
Alicia from Blue Roses
Prier
Kisaragi from Criminal Girls
The Unlosing Ranger