Two common peripheral interfaces are Firewire (400Mbps or 800Mbps) and USB2 (480Mbps). These are serial, so you've got incredibly high bit rates on the incoming pins; significantly higher than the clock rates of reasonable FPGAs.
Do there exist chips to convert an 800Mbps serial stream to a 50MHz stream of 16-bit words, and what are they called? I imagine it's not impractical to hook a couple of those and a couple of SRAMs to a single FPGA, stream in the signal and then read out little bits of it if you need to look in the stream for control signals.
The proposed application is wire-speed video capture to a Firewire disc from a Firewire or USB2 camera, using an FPGA in the middle to do the trivial things like dark-frame subtraction.
Tom