AT&T offers the OtterBox Armor Series Case for iPhone 4/4S in Black/Green for $5 with free shipping. That's $20 below last week's mention and the lowest total price we've seen for this case. (It's a current low by $20.) This waterproof case is purported to withstand a 10-foot drop, two tons of crushing force, and up to six feet of water for 30 minutes.

Update: It's now available for in-store pickup only and stock varies by ZIP code.