I'm surprised nobody has suggested
Monoprice. I suppose it's because they have no 9-pin firewire to iPod connectors, but neither does Apple for that matter, something I think is ironic because all their computers have FireWire 800.
I still think Monoprice is relevant to the discussion because if you ever find yourself in a place where you need to use a video camera or external firewire harddrive with you MacBook Pro, you can buy a 6 ft 9-4 pin cable and a 6 ft 9-6 pin cable for less than that Sonnet adapter. It's one of those things that when you need it, you really need it.
The reason why USB to FireWire adapters don't exist is because they use different methods of transferring data, not because of inter-corporate bigotry; USB transfers data in packets, in much the same way that DB-9 serial devices do, and in the way that (more modern) networking protocols and DisplayPort protocols transfer data. FireWire/IEEE 1394/i.Link transfers data sequentially; it does not use packets, and streams data constantly between devices. This is why FireWire is often much faster than USB and is mainly used for devices that must transfer large amounts of data, and USB is used by Bluetooth adapters, IR receivers, etc. In fact, the IEEE 1394 standard supports a 3.2 Gbps transfer rate, given enough pins.
