Sadly, these few resources are the only ones I know that are specific to syndication.  See also general copyright or trademark information.

Articles on Syndication

• Drafting Creator Contracts: A Practical Guide for Syndicates, Creators and Their Attorneys by Stuart M. Rees.  1998.
  This free 120 page article provides an overview of the business of syndication (30 pages) and an analysis of major syndicate contracts (90 pages).  Stu Rees is the only comic strip and text feature syndication contract lawyer specialist in the U.S.  His experience as a syndication attorney is described in a Los Angeles Daily Journal profile piece. 
• Making Money Cartooning: Meeting Notes from the June 2000 AAEC Convention by Stuart M. Rees, syndication lawyer.

Books on Syndication

• Successful Syndication: A Guide for Writers and Cartoonists
  by Michael H. Sedge (Paperback)
• Your Career in the Comics
  by Lee Nordling (Paperback – November 1995)

Comic and Text Feature Syndicates

The following six syndicates are typically viewed as the leading comic syndicates.  They also offer a diverse array of text and other features.

• Creators Syndicate
  Offers Submission Guidelines.
• King Features Syndicate
  Offers Submission Guidelines.
• Tribune Media Syndicate
  Tribune’s Syndication Information gives helpful information and tips.  See also Submission Guidelines.
• United Media: The Comic Strip
  Offers Submission Guidelines.   
• Universal Press Syndicate
  Offers Submission Guidelines. 
• Washington Post Writers Group.  
  Has several comic strips and a history of selecting good ones, like Bloom County and Non Sequitur.