Their website is weareamericaalliance.org, which redirects to cccaction.org/cccaction/waaa_home_page.html
A partial list of their members is here.
The National Council of La Raza has also joined. [1]
Immigrant Supporters To Counter Bush Speech says that the Central American Resource Center (CARECEN) as well as unnamed "Catholic churches" are also members of WAAA. That article also compares WAAA to more militant groups such as the March 25 Coalition.
There is also a group known as Somos America, which may or may not be the same organization (see SEIU Local 2028 document).
Forum to address impound law (tangential link to Mexican government)