On the heels of, today Mad Catz announced a similar, cheaper alternative that will provide your Xbox 360 with the same wireless capability. Priced at $80 it appears to be a no-brainer over the $100 Microsoft-branded adapter, and did we mention it works with the PlayStation 3, as well?
Instead of a USB interface, the Mad Catz adapter will have an Ethernet port, enabling you to use it with either console. Also in the box will be a 3.3-foot Ethernet cable, which should net you enough slack for optimal reception.
The Mad Catz Wireless-N Gaming Adapter is available via the GameShark store.