pretty much any wireless router will work..just depends on how much you want to spend vs quality of the router....i have a WRT54G and love it...you can get a wireless router anywhere from $10 to $150
Just make sure that you get a xbox live compatable router. It will make your life much easier.
Here is the list... http://www.xbox.com/en-US/support/connecttolive/xbox/homenetworking/compatible.htm I personally use the DI-624 for both and have had no problems over the last 2 yrs. I was able to purchase it from newegg with a rebate for around $25.