In beta Ocarina of Time there were medallions that had effects, rather than just sitting in the pause screen.
The Wind Medallion was Farore's Wind
Theory: Though there is relative proof to say that it wasn't called the "Forest Medallion" as there is unused kanji in the original Ocarina of Time that is called "Wind Medallion". It is doubtful that you would have received a medallion so early in the game, the Forest Temple is shown long before any shots of the in-development Deku Tree, which while the Forest Temple (or as it was probably once called "Wind Temple") stayed relatively the same throughout production, the Deku Tree was altered a few times.
The fire medallion had the same effect as Din's fire. It was obtained after beating Dodongo's Cavern.
Theory: The Fire Temple was probably at one time the Dodongo's Cavern, or perhaps Turtle Rock.... in any case, yes. Beta shows us hardly any of the Fire Temple, but the Dodongo's Cavern is shown in very early beta, it is no stretch of the imagination to say that one would recieve a Medallion from the area.
The Ice Medallion had a ice effect
Theory:In the beta of the game there was an Ice Medallion, I believe this has been cited in official interviews speaking of an Ice Dungeon they couldn't fully fit in, as well as the kanji for "Ice Medallion" found in the original Ocarina of Time. Not to mention hackers had recently found theoretical proof on the existence of an Ice Magic in the Damage Charts for enemies. (Damage from Link's various equipment).
The Spirit Medallion had the same effect as the Lens of Truth. It was obtained after beating the Spirit Temple.
The Shadow Medallion had the effect of Nayru's Love
Theory: The internal file name of Nayru's Love is "ovl_magic_dark", hinting that this was originally the function of the Shadow Medallion, which corresponds pretty well to where it was finally put in the game, under a normal progresssion one would go Shadow then Spirit, therefore right before the Spirit Temple is what they might have intended for the Shadow Medallion, it is a very late, game breaking item in a way.
The Light Medallion had a light effect harmful to enemies such as Dark Link. It was obtained after beating the Temple of Light.
Theory: Further proof from hackers show that the Light Medallion may have either given a Light Spell or Beam Blade itself. In the enemy damage chart, following Din's Fire and a supposed "Ice Spell", is another byte which normally has a dealing with a Light effect, and effective to a variety of foes. Namely Dark Link, which hints highly at it being a Light Spell/and or the Beam Blade's damage byte.
Zeth's Statements: Stated in Nintendo Power's guide is that the Bladebeam was given to link by the Great Fairy.