What are the .NET Micro Framework ready systems available?
TinyCLR produces several different boards that support the .Net Micro Framework, the most popular was once the Fez Domino, now deprecated and replaced by the Fez Panda II:


FEZ (Freakin' Easy!) is a tiny open-source board running Microsoft .NET Micro Framework. This means, you can write code with much more efficiency using C# programming language under free Microsoft Visual C# express. Build your next projects in minutes by connecting FEZ Domino to one of the shields or the many available components. Includes USB cable.
Many libraries are already included like FAT file system, threading, USB Client, USB Host, UART, SPI, I2C, GPIO, PWM, ADC, DAC and many more.
FEZ offers many features not found in Arduino, BASIC STAMP and others:

Based on Microsoft''s .NET Micro Framework.
Runs on 72Mhz NXP ARM processors.
Supports runtime debugging (breakpoints, variable inspection, stepping, etc.)
Use Visual C# 2010 Express Edition for development.
Advanced capabilities like FAT, USB device and USB host.
Easily upgrades to hardware such as EMX.
Open source hardware design files.
Use existing shields and holder boards.
Based on the USBizi chipset (ideal for commercial use).
FEZ Mini is BS2 pin-out compatible with extra I/Os.
FEZ Domino is Arduino pin-out compatible with extra I/Os.