FPGA based Synth Links
Here are a few links I have found that may be of interest. If you know of any more that you think should be here, please let me know.
Chris Strellis' FPGA Synth
Chris Strellis' Additive FPGA synth (based on the work of Samuel Nobs and Daniel Engeler).
Emulation of the infamous SID chip, using an external filter.