I ran into this very-informative Xilinx user guide about PCB layout; it’s specifically tailored towards people who are interested in mounting a Spartan-6 FPGA on a board, especially for high-speed use, but I found it to be a good introduction to PCB design for high-speed circuits (such as explaining parasitic inductances, how to determine them from datasheets, and how to minimize them in a final design).  Reading it actually got me pretty worried, since I’m hoping to be able to put together my own FPGA board at some point, and it made me realize that I definitely don’t have the experience or equipment to be able to even verify if I’ve met their guidelines.  Right now I’m just hoping that the FPGAs are robust enough, especially at the lower clock speeds I’m thinking about, to not require the full-blown techniques in this guide, since this guy seems to have been able to do it himself with no prior experience.