What is you PHY going to be like? Also, since you don't care about UDP or TCP, you could also consider raw ethernet frames. Depends a bit on what the spartan-6 is going to connect to. If it for example a direct utp cable to a PC that you have full control over (i.e no routing/switching), then you could do raw ethernet. That would mean less effort for programming the spartan-6.
Other than that, if you have already taken care of the PHY then the fpga4fun link is a good one.