Ending today, B&H Photo Video offers the Amazon Kindle 6" WiFi eBook Touchscreen Reader with Special Offers for $49 with free shipping. That's tied with our mention from three weeks ago (although that was limited to Amazon Prime members) as the lowest total price we've seen. (Outside of the mention below, it's a current low by $21.) It features 4GB of storage, Pearl e-paper technology, and a purported 4-week battery life.
A close price: Today only, Best Buy offers it for $49.99 with free shipping.