One tbs of Cod Liver Oil will give you 340% the recommended Daily value of D.
Seems like the most economical way to get the vitamin.
Cod Liver Oil also has Vitamin A. Too much Vitamin A can be toxic, and different brands of Cod Liver Oil have different amounts. Better to get Vitamin D from the sun, and second, from a supplement (Cholecalciferol-Vitamin D3).
Cod liver oil: http://www.vitamindcouncil.org/newsletter/2008-december.shtml