how much do you want to spend!? your best bet on that mobo is Phenom x6 1100T, if you can find any... you can go with AMD FX-Series as well, but only the bulldozer architecture which is not advisable, here is the list of CPUs you can upgrade to http://www.cpu-upgrade.com/mb-Gigabyte/GA-M68MT-S2%28rev._3.1%29.html ,
how much do you want to spend!? your best bet on that mobo is Phenom x6 1100T, if you can find any... you can go with AMD FX-Series as well, but only the bulldozer architecture which is not advisable, here is the list of CPUs you can upgrade to http://www.cpu-upgrade.com/mb-Gigabyte/GA-M68MT-S2%28rev._3.1%29.html ,