I am using the SuperPRO from Coridium
It is an NXP LPC1756 32bit ARM M3Cortex development board fro $49. They have one for $35 also. 52 IO. I think Dale and Clint are using similar ones to the ARMexpress boards at the bottom of the page and I think they were the NXP 1768 chip. It comes with a free C or BASIC compiler and I use Notepad++ for writing the programs. I am still at the beginning stages of learning it so I can't provide much help. There are some nice Yahoo groups for it though(ARMexpress).
I plan on eventually using the Arduino Pro which is the same form factor and can attach the Coridium board for off board processing