This is an excellent compilation... just like @Max The Magnificent says below, it would have been great if these were available even 10 years ago, would have made serious changes to my career! I also see some one below commented on TI's Launchpad which is another good one for school kids to play with (and some grownups watching & wishing!).
These kind of development boards not only help the engineers, but also help the students and electronics enthusiasts to develop innovative staffs at a very low cost. About 12 years back I bought a 8951 board which was 10-15 times larger than these boards and I paid ~$100. I used that a lot learning and doing several home automation staffs. The enthusiasts now can do much more with these tiny things without spending more money.
@Caleb: Someone brought the Jeenode to my attention...
The frustrating thing for me is that I would have killed to have this sort of thing when I was younger, but there was nothing like these boards available -- and now that they are available (and affordable) I simply don't have the time to play with them (sad face).
Much of the limit to size is sensibly getting useful signals in and out.
None of these boards have gone to die-bond and globbing.
Using standard parts (not bare) I laid out a board a few years ago with a TI uBGA MSP430 DSP on one side, a DFN EEPROM on the other, several OPAs and a bunch of related discrete, thermistors and a pressure sensor, all on 19mm x 6.9mm.
Not a development board, of course, but not pushing the shrink limits all that hard, either. (wildlife telemetry fwiw).