Seems like I'm always finding more Arduino-compatible boards to add to the spreadsheet-- added four today, bringing the current count to 89. I remove some occasionally when I check and find the links are no good, but hopefully all of the listed boards really are available, or will be very soon.
Added today are Duemilanove and Mega clones from DF Robot, a Chinese company, as well as their Romeo robotics board (pictured, $36) which is essentially a Duemilanove with the SMD ATmega328's 2 extra analog pins exposed (Seeeduino style), male header pins, on-board buttons, I2C headers, and an L298 motor driver with screw terminals.
Also added is the Displayduino (pictured, $70, which I noticed at Sparkfun), the core of the MondoMatrix modular system for controlling large numbers of LEDs or servos or whatever. Displayduino acts like a Sanguino with USB, screw terminals, and an RS485 port driver for communication in addition to the ATmega644's two UARTs.