Mwave offers the MSI X99S Gaming 9 ACK LGA 2011 Intel X99 E-ATX Motherboard for $419.99. This $25 mail-in rebate cuts that to $394.99. With free shipping, that's the lowest total price we could find by $23. It supports Intel Haswell-E and -EP CPUs and up to 128GB RAM; it also features five PCI Express 3.0 x16 slots, 4-way SLI, 802.11ac wireless, Bluetooth 4.1, and Gigabit Ethernet. Deal ends July 31.