MSI P67 GD65 v G45

GD65 has more power phases for the CPU.
GD65 has Hi-c Tantalum core capacitors.
GD65 has Super Ferrite Chokes for the memory.

The above three items means GD65 has a better power system for overclocking.

GD65 has 4x SATA3, 4x SATA2, and 2x eSATA ports.

The only advantage G45 has is 2x USB2 internal headers, so you can have four USB2 ports on the front/top of the case. GD65 only has one USB2 header, so it can have two USB2 ports on the front/top.

If you're not going to overclock, need only two SATA3 ports, and don't need eSATA ports, then G45 would be a good choice. If you are going to overclock, GD65 is much better.