If you have no money, then the best overclocking board is the one you have ......
Otherwise are we talking Athlon or Tbird or Duron or K62?
Athlon: Abit KA7, Asus K7M
Tbird/Duron: A7V133, Abit KT7A or KT7A Raid, MSI K7T Turbo, Epox 8KT3A, Iwill KK266. All are good and will overclock, a less expensive one that will do it decently is and of the KT133 versions of the above boards or a FIC AZ11E.
K62: Epox MVP3G2 or G5, Asus P5A
A good overclocker board and HSF will cost you no less than $150 USD.... probably about $100 for a K62 OC board.... heck I'll sell you mine. (Epox G2, K62 500)