I have been using an olimex ARM-USB-OCD-H from my linux box to program fpgas. I bought a RaspberryPi and was able to run openOCD on that to program using the olimex as well.
There are several fpga boards available for the RaspberryPi and some are as low as $35. I am considering doing an opensource hardware project to create an fpga and linux image with openocd running on the Pi. For about the same price for one of these these usb based jtag controllers you could get an embedded arm processor with ethernet connectivity and lots of buffer ram to drive a hardware optimized jtag controller. It would all be off the shelf hardware.
I am wondering if anyone else would be interested. My expertise is in hardware design and I could use someone who knew their way around a device driver.
John Eaton