If you've got an Xbox 360 Slim 250gb and need to transfer the data to your new limited edition Gears of War 3 Xbox 360 Slim 320gb, Call of Duty Modern Warfare 3 Xbox 360 Slim 320gb or Star Wars Xbox 360 Slim 320gb, you've got 2 options:

Official Xbox 360 Data Transfer Cable *Quickest*



Microsoft has announced a new Xbox 360 Slim Data Transfer kit which is due for release on the 10th/11th October 2011 (purchase link will follow upon release).

Transfer content via USB Drive (Memory Stick) *Slowest*

The considerably slower option is to transfer data from one console to the other using a USB Drive (Memory Stick). The current highest capacity of space that can be used is 16gb (the minimum is 2gb) and it needs to be formatted on an Xbox 360 to be Xbox 360 content compatible. Backup everything you want off of the USB Drive (Memory Stick) before you do this, as it will wipe all content.You can then transfer data from one Xbox 360 Slim to another Xbox 360 slim in chunks of up to 16gb at a time (well 14 odd gb due to the actual usable space on the USB Drive).

If you need a USB Drive (Memory Stick) I personally recommend:

Kingston DataTraveler 101 Gen 2 16GB USB Drive - Kingston DataTraveler 101 Gen 2 16GB USB Drive - Black: Amazon.co.uk: Computers & Accessories
SanDisk Cruzer Blade USB Flash Drive 16GB - SanDisk Cruzer Blade USB Flash Drive 16GB: Amazon.co.uk: Computers & Accessories