BBuy Reward Zone Members to Get iPhone Discount
Premier Silver Members are those who have spent $2,500 at Best Buy during a single calendar year; they are automatically upgraded from the normal membership level. Membership is free, by the way.
This brings the price of an 8GB iPhone 3G to as low as $99, while a 16GB iPhone 3G would be $199 for a Premier Silver Member.
These are discounts for new phones, not refurbished ones, as well. It's in-store only, however, and requires the obvious two-year service agreement. Also, you need to be eligible for an upgrade to your current phone.