Most of the midrange and up nForce 500 and 600 series boards should overclock pretty well. For example, even my MSI K9N Platinum Rev 1.0 (one of the first AM2 boards ever released) will do a stable 290HTT on my X2 3600+, which only has a 9.5x multi. With your unlocked multi, 2.8+ GHz shouldn't be hard with any decent board from one of the big makers like MSI, Asus, etc.