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The Terasic series are great, especially if you aren't too fussed about peripherals on the board. The DE0-nano has a decent sized FPGA and SDRAM for less than $100. There is also a SoC variant of this board coming soon with an integrated ARM subsystem.

I've recently purchased the parallela board:

http://www.parallella.org/

It's got USB/ethernet/arm cpu , and has been incorporated into numerous other projects. It's ~$100.00 USD.

I second the parallella, not only does it have an FPGA, an arm core and a massively parallel cpu. So much to play with and still running Linux so the workflow is super smooth.

http://valentfx.com/logi-pi/ (or logibone) is reasonably good, it's a Spartan6 LX9, easily programmable via SPI, and you can communicate with your design using the same SPI, easily clocked up to 30mbps.

For bigger designs (e.g., a full OpenRISC SoC fits, with ethernet and VGA and all that) you can use Digilent Atlys board, it's cheap for students (although communicating with it is a bit more complicated).

Probably the Zedboard.