The stock Intel HSF should be fine for "mild" OC'ing.
If you do want to go with an aftermarket HSF, these two are equal in cooling performance and are about the same price. The Zalman requires removal of the Mobo for installation and the Arctic Cooling does not. The AC has a 4-Pin plug and I "believe" the Zalman uses a 3-Pin plug.
ARCTIC COOLING Freezer 7 Pro $31.99 /free shipping.
http://www.newegg.com/Product/Produc...82E16835186134
ZALMAN CNPS9500 $32.99
http://www.newegg.com/Product/Produc...82E16835118003