Complex sentence: Large donors also contribute a substantial portion of the organization's budget; past donors have included the Bill & Melinda Gates Foundation, Buffett Foundation, Ford Foundation, Turner Foundation, the Cullmans and others.
Split into simpler sentences: Large donors also contribute a substantial portion of the organization's budget. Past donors have included the Bill & Melinda Gates Foundation, the Buffett Foundation, the Ford Foundation, the Turner Foundation, the Cullmans, and others.