This is for an '03, NA CC Auto LWB. I'd prefer OEM, but they seem kinda pricey in my first rudimentary search. It's the 1st one in the exhaust flow on the passenger side.
NTK (which is part of the same company that makes NGK spark plugs) is the original equipment supplier of oxygen sensors and air/fuel ratio sensors to Nissan. Denso, which is owned by Toyota, also makes good oxygen sensors and plugs.