There's a nice book called FPGA Prototyping Using Verilog Examples (also available in VHDL), which was written for Digilent's Nexys2 board, but some of the examples might apply. The ATLYS looks great for your application, gonnafail, and also mine - thanks allanw, I might actually redesign the thing I'm in the midst of making for the Nexys2 to use it, because it has a nice impedance controlled, matched differential pair connector. The Nexys2's expansion port has arbitrary length traces and differential pairs are scattered every which way!