I bought the ADS HDTV Upconverter II HDUP-1500 a couple of years ago since my TV is 1080i only. It looks like that model is discontinued now, but you may be able to find a used one. I only paid $250 after rebate for it brand new and shipped.
The only downside is that it does not support...
computers4sure.com has great deals on Xbox 360 accessories as well.
Microsoft Xbox 360 Wireless Networking Adapter - $87.99 with free shipping:
http://www.computers4sure.com/product.asp?productid=3452117&iid=1249&Hits=7&HKeyword=xbox+360+wireless