Smithsonian Institution
National Museum of Natural History: Ocean Planet: Ocean Currents
The Ocean Planet exhibit at the Smithsonian explains the general features of ocean circulation. A general look at upwelling, deep water, and currents are combined for an overall view.
US Navy
Office of Naval Research: Ocean Currents
Probe the basics of ocean currents and be ready for the "quick quiz" upon completion of your reading. A concise and effective site supplemented with drawings.