Not just the chipKITs, Renesas has a board available in Asia and Europe that could be a pretty serious contender for the *duino compatible crowds. 100MHz 32bit uC with floating point can do some amazing stuff. The biggest difference is how it access memory etc and trying to get past some of the Harvard arcitecture issues to the hybrid that Renesas has in the RX series MCUs is where most of the stumbling blocks seem to occur.
Hmmm, Cypress' $25 PSCO4 Pioneer Kit has both PMod & Arduino shield connnector - and reconfigurable analog, yay! OTOH, it's not Arduino software compatible, although IIRC Cypress has some point & click development choices.
Yet another choice is the Papilio FPGA board, which tries to be pretty Arduino compatible, although I'm not sure its as slick as the chipKits, but has the added speed of the ZPUino core (32-bit, 96MHz, large code space) and, of course, FPGA flexiblity.
The chipKit Pi+ RPi combo is pretty affordable, not much more than an Arduino Due. So many good choices, so little time.
BTW, do you have any links to TI or Maxim PMods? I tried finding some last week & couldn't.