Primary markets - grassroots nonprofit organizations, social change groups, political organizations, groups doing community organizing. Most specifically, groups working on economic justice, anti-racism, gender equality, LGBTQ rights, and immigrant rights. Many are political active and do voter registration and grassroots advocacy work. I would say the central theme is around building political power and organizing for justice - long-term structural change, rather than immediate relief through services.
Secondary markets - social service agencies, community arts centers, health care agencies, education centers. These are groups providing more immediate and direct services - homeless shelters, domestic violence services, soup kitchens, elder care facilities, ESL and adult education classes, community health centers, art programs for kids, etc.
Also should appeal to other nonprofit consultants in the position to refer clients, nonprofit training centers providing workshops to potential clients, etc.
The clients I work with are - predominantly women, politically engaged and progressive, racially diverse, community-based, financially-strapped, stressed, overworked, doing at least 2-3 jobs within their organizations, worried about the economy, and are coming from very small shops with few staff dedicated to fundraising.