Microcenter is offering a $100 rebate off of either the Core or Premium Xbox 360 systems. Currently, there are none in stock online, so a local visit will be required (18 stores in the U.S.). Rebate expires 12/31/2006.
Steps:
1. Find a store near you
2. Purchase the system
3. Print the rebate (Microcenter)
4. Mail the rebate, copy of receipt, and copy of UPC
5. Wait 8-12 weeks
[Thanks Lord Slappy & b0gard & ericheaf]