GD65:
-- 2 PCIe 2.0 x16, 4 x1 slots
-- 8 USB 2.0 ports in rear
GD80:
-- 2 PCIe 2.0 x16, 1 x8, 1 x4, 2 x1 slots
-- 6 USB 2.0, 2 eSATA, 1 IEEE 1394 ports in rear
-- Supports 3-way SLI
Other than that, they're identical: 6 SATA III controllers, 2 USB 3.0 ports on the back, support 2-way SLI/CrossFire, 4 dual-channel RAM slots (max of 8GB/slot, 32GB overall), support RAID 0/1/5/10, 6 audio ports plus Optical & Coaxial SPDIF ports, & built-in Gigabit LAN port.
Note that, while the descriptions claim that the GD80 doesn't support FX-series processors, the Support tab lists the FX-series as being supported on the board.
Also, while the GD80V2 seems nearly identical to the GD80, the GD65V2 is not (has 1 x16 and 1 x8 PCIe slot in place of the 2 x16 slots; only supports FX-41xx/61xx/81xx series processors at best).