Here's  a collection of books, online articles and other resources which might be useful for developing portals and grid portals.

BOOKS 

• Proven Portals: Best Practices for Planning, Designing, and Developing Enterprise Portals http://safari.oreilly.com/0321125207
• Beyond Java http://safari.oreilly.com/0596100949
• Building Portals with the Java Portlet API ISBN: 1590592840 416 pp. Published: Aug 2004 Price: $49.99 eBook Price: $25.00
• IBM WebSphere Portal V5 A Guide for Portlet Application Development http://safari.oreilly.com/0738498513
• Architecting Portal Solutionshttp://safari.oreilly.com/0738498645
• IBM Rational Application Developer V6 Portlet Application Development and Portal Tools http://safari.oreilly.com/073849352X
• Globus Toolkit 4 by Borja Sotomayor and Lisa Childers, ISBN-10: 0-12-369404-3 Morgan Kaufmann Publishers
• There is an excellent book, Portlets and Apache Portals, by Stefan Hepper and others, by Manning Publications, which unfortunately was not published as a book, but is available for free download from http://www.manning.com I found the book to very good.

ARTICLES

• Clustering Tomcat: http://www.ja-sig.org/wiki/display/PLT/Clustering+JSR-168+Portlet+Applications+in+Tomcat
• Ajax and Portlets: http://developers.sun.com/portalserver/reference/techart/asynch_rendering.html
• Development of standards-based grid portals, Part 1: Review of grid portals http://www-128.ibm.com/developerworks/grid/library/gr-stdsportal1/?ca=dnw-812
• Use Dojo, an open-source JavaScript library, to add client-side inter-portlet communication to your portal applications. http://www-128.ibm.com/developerworks/websphere/library/techarticles/0703_wallaker/0703_wallaker.html?ca=dnw-812
• With XML, reuse existing Java code and define a Web service using WSDL and JiBX definitions that accurately describe your Java classes. http://www-128.ibm.com/developerworks/xml/library/x-jibx1/?ca=dnw-812
• The busy Java developer's guide to db4o: Introduction and overview http://www-128.ibm.com/developerworks/java/library/j-db4o1.html?ca=dnw-812