Amazon offers the Gigabyte Gaming Intel Z170 LGA 1151 ATX Motherboard, model no. GA-Z170X-GAMING 5, for $141.75. Redeem this $20 mail-in rebate to cut the price to $121.75. With free shipping, that's the lowest total price we could find by $20. Features include four PCIe 3.0x1 slots, one PCIe 3.0x4 slot, one PCIe 3.0x8 slot, one PCIe 3.0x16 slot, three SATA express connectors, and six SATA 6Gb/s connectors. Rebate expires February 28.
Update: Specs corrected.