Just this month 1BOG launched Los Angeles and after the great success of the San Francisco BOG (which attracted over 1,000 homeowners) they are expecting a large order to come to LA.
1BOG has a great info site and field kit featuring their cute little green guy (the Bogman), and have an open invitation for volunteers who want to organize a group solar purchase. They also have a large interactive map which includes all 20 cities that currently have a 1BOG program. You can zoom in and see where other homes have joined in (though all addresses are kept private):
In Europe, especially in Germany, these types of group purchasing programs have been used in conjunction with Feed-in Tariffs and are largely credited with their rapid adoption rate of domestic solar energy.