I've been getting interested in the Parallax Propeller chip lately and decided to dive in by designing a breakout board for the chip. I based my design on the reference designs given by Parallax so nothing really new there. I decided to include an EEPROM chip on the board so that programs could be stored between power cycles. For a development board, this wouldn't be strictly necessary since you can always use your host computer to download code into RAM instead. But I decided to add the EEPROM since it doesn't add that much to the cost and it allows you to use the board in stand-alone applications. The parts cost for this design, including the board from Laen's PCB group order, is around $13.
For those not familiar with the Propeller, it is an interesting design. The chip has no interrupts. Instead, multi-threading is handled by using the eight 32 bit cores (called cogs), which share a 32KB central memory in a round-robin fashion. Each core also has a smaller amount of dedicated memory. The typical clock rate on a Propeller is 80MHz and most instructions take 4 cycles so each cog runs at roughly 20MIPS. As opposed to, for example, a typical AVR chip, the Propeller doesn't have much special purpose hardware: no SPI or I2C, no hardware multiply or divide and no ADCs. Each cog does have two timers and can do PWM output. Each cog also has access to all 32 GPIO pins and there are available codes for doing things like SPI, UART and I2C via bit-banging at pretty high speeds so the lack of special purpose hardware isn't as big of a limitation as it might appear at first. The cogs also have hardware assistance for video signal generation which might be handy sometimes.
The official Parallax software is available for Windows and a free alternative (http://www.fnarfbargle.com/bst.html) is available for Linux, Windows and Mac. The "native" language for the Propeller is an interpreted language called Spin but there is also a free C compiler available (http://catalina-c.sourceforge.net).
I've attached the Eagle files for the latest revision of this board. The only differences with the one in the photo are the number and placement of bypass capacitors.