• Comparison to Struts
• Comparison to JSF
• Comparison to Tapestry
• Comparison to Spring MVC
• Comparison to Ruby on Rails

Matt Raible wrote (mid 2005) an interesting whitepaper where he compared various web frameworks. You can view the PDF here:
https://equinox.dev.java.net/framework-comparison/WebFrameworks.pdf
http://www.virtuas.com/files/osl-jwf-01.pdf