Parallella: an Open Multi-Core CPU Architecture
First time accepted submitter thrae writes "Adapteva has just released the architecture and software reference manuals for their many-core Epiphany processors. Adapteva's goal is to bring massively parallel programming to the masses with a sub-$100 16-core system and a sub-$200 64-core system. The architecture has advantages over GPUs in terms of future scaling and ease of use. Adapteva is planning to make the products open source. Ars Technica has a nice overview of the project."
The Parallax Propeller is a great multi-core chip to get started with. The chip is $7.95 and has 8 cores running at 80Mhz. You can pickup the Quickstart board at Radio Shack for $40, including an overpriced RS USB cable (they normally retail for $25).
The Parallax Propeller is a much more economical way of getting started with multi-core programming. Parallax offers the PropTool, which provides SPIN and PASM language support. For C development you can get SimpleIDE which is a great IDE to get started with C programming on the Propeller, which uses a port of GCC.