What other groups are participating and who is the organizer?
Actually, the way I understand it, there are several events planned during this time period of Sept 10 through Sept 13, organized by various grassroots organizations. The 09-12-09 March on Washington is just one. The National Sponsor is Freedom Works Foundation.
Here is the organizer’s official page:
The list of co-sponsors is growing.
You should be able to find the answer with these keywords:
There is an update on the 912DC website and I posted a thread on it a few minutes ago.
Update on the March (July 15th)[09.12.09 March on Washington]