Pendant of Virtue

The Pendants of Virtue appear in A Link to the Past and are required in order to retrieve the Master Sword. Link must travel to three dungeons and collect each one before going to the Lost Woods to find the Master Sword. An ancient Hylian verse on the pedestal of the Master Sword about the pendants reads:

"The Hero's triumph on Cataclysm's Eve Wins three symbols of virtue. The Master Sword he will then retrieve, Keeping the Knights' line true."

The Pendents
Pendant of Courage The Pendant of Courage is located in the Eastern Palace in (unpredictably) the East of Hyrule close to the cave that Sahasrahla is hiding in. It’s guardians (the temple bosses) are a group of six Armos Knights.

Pendant of Power The Pendant of Power is found in the The Desert Palaceis the south-west of the map. The dungeon bosses are three Lanmolas. Oddly this Pendant is blue while other items associated with power or Din (such as Din's Pearl or the Goron Ruby) are coloured red.

Pendant of Wisdom The Pendant of Wisdom is Located in the The Tower of Hera atop Death Mountain. The guardian of the final Pendant is a single Moldorm. Like the Pendant of Power this pendant is a different colour than other items similar to it (such as the Zora's Sapphire or Nayru's Pearl). It is red.

Theory
Some have noted the similarities shared by the Pendants of Virtue, the Goddess Pearls and the Spiritual Stones. This could indicate a direct link between these artifacts, or equally it could simply be an example of the designers' desire to create a feeling of familiarity or a sense of a "shared legend" within the series.