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:

Patterns: SOA Foundation - Business Process Management Scenario, SG24-7234-00

Redbooks, published 8 August 2006, last updated 11 August 2006

Patterns: Building Serial and Parallel Processes for IBM WebSphere Process Server V6, SG24-7205-00

Redbooks, published 23 April 2006, last updated 25 April 2006

Microsoft BizTalk to WebSphere Business Integration Server Express Migration, SG24-7142-00

Redbooks, published 24 March 2006, last updated 13 June 2006

Build a Business Process Solution Using Rational and WebSphere Tools, SG24-6636-00

Redbooks, published 24 February 2006

You can search the RedBooks site for anything related to BPEL by clicking the link below.