Spartan 3E Starter kit
Xilinx Spartan 3E (500K gate device), 50Mhz on board clock, 128Mbit flash, 16Mbit SPI flash, 64Mbyte DDR SDRAM, 4 channel 12 bit DAC and dual channel 14 bitADC.
Ethernet port, USB (for JTAG/programmer), two RS232 connectors, PS2, VGA, HiRose, ADC in, DAC out.
20 by 2 LCD, rotary encoder, 4 momentary switches, 4 slide switches, 8 LEDs.
This board seems to have kicked off a spur of enthusiasm amongst SynthDIYers around the globe. Basically it has everything you need to get you going and build a synth.
Coupled with all the nice features, like DAC, ADC, memory and built in JTAG programmer, it also has a large FPGA.
3E starter kit, The Xilinx page which has a host of information and documents.