There are numerous books now available on how to plant churches, covering many different styles of churches. However, there have not been many resources specifically designed for churches which want to sponsor the planting of other churches. Spin-Off Churches: How One Church Successfully Plants Another by Rodney Harrison, Tom Cheyney and Don Overstreet is a book which aims to address this issue.
Part 1 of the book covers the fundamentals of sponsoring churches. Part 2 covers attitudes towards sponsorship. Part 3 provides advice on finding a church model that fits. Part 4 describes the phases of new church development. Part 5 relates to finding the resources. Part 6 relates to the relationship between the sponsoring church and the new church. Part 7 describes ways of promoting the idea of becoming a sponsoring church.
The book contains plenty of useful material, but like most books written by multiple authors, although it contains many interesting details, I found it fairly heavy going as a whole. I think it would be useful to churches which are already excited about planting other churches, but it is unlikely to be sufficiently inspiring to capture the imagination of others.