Well, even if you do build your own custom controller form scratch - in order to market it, your fears of 'patent rights' might come back to haunt you. Although I don't think any wireless protocol you use is copyrighted, the way in which the 'dongle' that plugs into the Xbox might be.
Many chinese companies sell stuff like this on ebay, that are fully comptable, and they don't seem to get in trouble though - so if I were you, I would just hack one. Be it an oficial wireless controller, or a knock-off. That'll handle ALL the wireless bits for you, leaving you to simply add your own signals to the controllers 'internal micro' - essentally replacing the analogue sticks and buttons.
But as yo're woried about patent issues, then I'm assuming you wish to market such a product, and mass produce. In which case you should do your research into short-range wireless comms. There are many 2.4hz transciever chips around (TI's chipcon, Nordics NRF24L01, atmel has a few) as well as modules for Zigbee. Also, as you're marketting the product you probably know a thing or two about microcontrollers and embedded electronics, or have to funds to hire an engineer to develop a prototype for you, so I'm not entirely sure what you're asking for?
If its a custom thing just for you and maybe a few friends, don't worry about patent issues, its by far easier to just buy a finished product and treat it as a 'group of modules' you can take apart, and modify for your own purposes.
Btw, I am totally unaware if the xbox 360 uses wireless controllers based on bluetooth or a built in proprietary system. If it uses BT, then you can simply by your own bluetooth modules, but you would need to know the specifics of the Xbox's BT end in order to communicate with it. If its a custom job, then you would need to contact microsoft and enquire about creating your own controller so they can provide the necessary info
All the previous answer was based on just a 'controller' and a 'dongle' that you physically plug into the xbox - I seriously doubt that approach would infringe on copyright.