Of course, we are interested in exploring what mobile computing in general has to offer teaching enhancement so I am listing here tablets other than iPad2, which are said to offer other kinds of features and/or additional power and storage. Please see a very useful article on Appolicious at http://www.androidapps.com/tech/articles/10206-the-best-tablet-alternatives-to-the-ipad-2 .
As of November, 2011 but not meant to be comprehensive:
Amazon Kindle Fire
B&N Nook Tablet
Samsung Galaxy Tab (7-inch, 8.9-inch or 10.1-inch screens)
HP Slate (Windows 7 software)
Lenovo Thinkpad
Asus EE Pad Transformer Prime (10.1-inch 1280×800 touchscreen, 1GB of RAM and 32GB ( or 64G) of storage )
Toshiba Thrive
Archos 70 or Archos 101
The Freedom 10 from Androidworldusa.com. Theirs is 10″, has 2 USB I/O ports, a HDMI port, full browser, Android apps, Mini-SDcard slot and half the cost ($249) of the iPad2 and Galaxy.