Best Buy is offering $50 off an iPhone 5 with a two-year-contract from either AT&T, Verizon, or Sprint. The deal is valid across the entire range: the 16GB ($149.99 with discount), 32GB ($249.99), and 64GB ($349.99) GSM and CDMA models.
We had a look around and there's currently a good amount of stock left all over the country. While some color / carrier combinations are not eligible for home delivery, every model seems to be widely available for in-store pickup. It's not absolutely clear how long the deal will run for, but some of the 16GB models are included in Best Buy's December 10th-11th sale page, so if you're interested we'd recommend getting your order in before Wednesday.
Update: a reader just got in touch with some more info on the offer. It'll run through to January 5th 2013 and the $50 discount is also applicable to any iPhone 4S.
Update 2: If you want another retailer option, RadioShack is also now offering $50 off the iPhone 5 or 4S on any carrier, apparently for in-store purchases only. We're not sure how long this one will last; if you buy before December 17th, you'll also get $10 back for every $50 spent.