For the 2005 Prius (NHW20), the original spark plugs are Denso IK16TT or NGK LFR5A-11 (long-life iridium). In both cases, this is the part number that corresponds to the 1.5L 1NZ-FXE engine.
Be careful not to use just any "equivalent" spark plugs: the engine is quite sensitive and it can affect misfires and fuel consumption. I would recommend using original Denso or NGK plugs, and they are normally changed around 150,000 km (or according to your service manual).
However, check the exact spacing and reference in your manual or with your VIN number at a dealer before ordering.