I wish someone would build for mashups what's out there for wikis at
http://www.wikimatrix.org/. In fact, I thought about it but someone is already squatting on mashupmatrix.org
Dion Hinchcliffe's article you mention is a good start, but a little dated. There are so many tools know it seems I learn about a different one each day. Just off the top of my head there's
JackBe, Denodo, Kapow, IBM Mashup Center, OpenSpan, Convertigo, Connotate, Serena, Lansa, Chickenfoot, WSO2, MindTouch, Dapper...
Dion includes some stuff in the RSS space which I'm skipping - but I include some stuff in the browser (chickenfoot) and wiki spaces (MindTouch).
The only way to really compare them is to put some thought into what you want to do (<plug>which my book hopefully helps you to do</plug>).
To illustrate some of the differences...
Need to mashup data coming from mainframes? Lansa or Convertigo are where to look..
Want to API-enable a clsoed web source? Most likely Kapow, OpenSpan, or Convertigo
Want to mashup various workflow-centric problems? Serena shines in this area
Want to give end-users the ability to build their own mashups? JackBe and IBM are probably the best tools to look at
Data mashups your bag? Denodo
Need to give end-users the ability to mark up web pages, hand them off to IT, and get solutions back? This is something interesting that Connotate does
As you can see, no particular tool does it all. I like the idea of starting with the Patterns you want to implement, and then backing into the right tools afterwards. Someone once came up to me and announced they were doing a pilot with vendor product X. Then I asked.. "What problem are you hoping to solve?" From their answer, it was clear they chose incorrectly. That's the danger when you start with tools first, and problems second.
How many of us just decided to learn Java for the heck of it, and how many did so b/c they had a problem to solve first?