What is the Most Effective Classroom Technology?

This is the million dollar question!  Like most educators in the blogging world I see the inherit value in educational technology.  Combined with sound pedagogical practices, the effective integration of technology has the ability to engage learners in a variety of ways.

The other day I came across this article where interactive whiteboards (IWB's) were touted as the most effective piece of classroom technology followed by individual netbooks for each student (these were being used predominately as e-readers).  The rationale for placing IWB's at the top of the list included the ability to manipulate virtual objects/data and cater to multiple learning styles (tactile, visual).
So what is the most effective classroom technology? Opinions will vary, but here is mine.  I believe for a specific type of technology to be successful in a classroom it must be multidimensional, cost-effective, easy to use, readily accessible by all, and most importantly engages students.  My choice is mobile learning devices, otherwise known as cell phones.  Let's face it, virtually every child possesses one of these powerful devices making it a cost effective option.  Many can be used as a research tool similar to a computer or as a student-response system when combined with a free Web 2.0 application like Poll Everywhere.  Like IWB's, they cater to both tactile and visual learners.  Add in the fact that kids love using them in school for learning makes this a compelling choice in my eyes.

So I would love to hear your opinion on this!  What do you think is the most effective classroom technology and why?