The Baptist Association by John A. Kohler
Nathan Finn has several links:
What Does it Mean for Local Baptist Churches to Associate Together?
Models of Baptist Associationalism
The Rationale for Baptist Associations
More Associational Nuggets
The Baptist Association ... Then and Now, a publication of the North American Mission Board (pdf document)
The Independency of the Local Church by E. L. Bynum
A Consideration of Baptist Associations: Why Were Baptist Associations Originally Established? by Robert L. Stovall
A Theological Rationale for Baptist Associations by Philip R. Bryan
Summary of Mike Day on "The Future of Baptist Associations and State Conventions"