BPEL-related IBM RedBooks
IBM has been an advocate of BPEL since the beginning, and IBM RedBooks have a number of books that discuss BPEL and various IBM tools and technologies. Most all can be downloaded, free of charge, in PDF format.
Please note that both the products and standards mentioned may have newer revisions. Please check both IBM product versions and BPEL standards versions.
Here are a few of the recent books you may find of interest:
Redbooks, published 8 August 2006, last updated 11 August 2006
Redbooks, published 23 April 2006, last updated 25 April 2006
Redbooks, published 24 March 2006, last updated 13 June 2006
Redbooks, published 24 February 2006
You can search the RedBooks site for anything related to BPEL by clicking the link below.