I was told by many that regular old, unscented, mineral oil for fretboard oiling.
http://www.cvs.com/shop/product-deta...p?skuId=152355
That above will probably last you a life time for oiling fret-boards (you only use a very small amount and only oil it once in a while.. maybe 1 or 2 times a year max. over-oiling can be just as bad as bone-dry)