Microsoft Store offers the 5.5-lb. Lenovo IdeaPad Flex 2 Signature Edition Intel Haswell Core i5 1.7GHz 15.6" Touchscreen Laptop in Black, model no. 59426101, for $499 with free shipping. That's $100 under our mention from a month ago and the lowest total price we've seen for any Lenovo Flex 2 with a 1080p display. (It's also $160 under the best price we could find for a similar model elsewhere.) It converts into a touchscreen tablet and features an Intel Core i5-4210U 1.7GHz Haswell dual-core processor, 15.6" 1920x1080 (1080p) LED-backlit touchscreen LCD, 6GB RAM, 500GB hard drive with 8GB SSD, 802.11n wireless, Bluetooth, webcam, 4-cell battery, and Windows 8.1 64-bit.
Note: It's not guaranteed for delivery by Christmas.