The Teensy 3.0 is now entering general release if you wanted an ARM board in a smaller package than the DUE. The Teensy is not the DUE, so be sure to understand what it offers and what it doesn't. Teensy 3.0 uses a modified Arduino 1.0.1 IDE.
I have one at home, awaiting torture. I can't tell you how excited I am about these little gems. The teensy is aimed at a much smaller market but I also happen to think that the Due is not only overkill but that it's design misses the sweet spot by virtue of shoehorning a 32-bit architecture into a 8-bit legacy interface. This 144-pin monstrosity seems to have been selected because one could put out a board in a similar I/O factor configuration as the Mega. But IMO they should have broken from past shield designs for the 32-bit architecture to eliminate the possibility of fried CPUs, enable improved I/O interfacing, among other issues.
For me, the 64-pin chip on the teensy offers plenty of I/O out of the box while still being bread-boardable. And the chip is 50% less to buy than the SAM processor on the Due, i.e. about the same price difference as a 328 vs. 1284. And the teensy price vs. Due price reflects that too. I am considering re-designing my DAQ boards around a standard dual pin header for the Teensy. It would eliminate a lot of the complexity from my boards and the CPUs can be re-purposed as needed later. Never mind the on-board RTC, 16-bit ADC (vs. 12 on the Due) etc.
But! There is something to be said for the benefits of older 5V-based legacy devices in terms of their ability to drive signals, etc. in ways that the more modern chips cannot.