Proto Drakes

First off, the definition of the prefix proto is as follows:

A combining form meaning "first", "foremost", "earliest form of" used in the formation of compound words.

Proto drakes are ancestors of the original drakes. Anyway, this guide will tell you of all the Proto-Drakes you can get, and even the ones no longer in game.

Reins of the Blue Proto-Drake (Added in Patch 3.0.2)

This mount is obtained through the Heroic version of Utgarde Pinnacle. It drops off of the third boss in the instance, Skadi the Ruthless. As of 11/25/11, Wowhead has this item listed at a 1.3% drop chance, meaning it is rare. But the boss is often soloed by players to not only earn the drake, but to also try and earn the two achievements tied into the boss, My Girl Loves to Skadi All the Time and Lodi Dodi We Loves the Skadi, both of which are needed for Glory of the Hero.

Reins of the Black Proto-Drake (Added in Patch 3.0.9, Removed in Patch 3.1)

This mount was the reward for Glory of the Raider (25 Player), but was removed in Patch 3.1 when Ulduar was released. All players that obtained the mount are allowed to keep it.

Reins of the Plagued Proto-Drake (Added in Patch 3.0.8, Removed in Patch 3.1.

This mount was the reward for Glory of the Raider (10 Player), but was removed in Patch 3.1 when Ulduar was released. All players that obtained the mount are allowed to keep it.

NOTE: The achievements for the last two Proto-Drakes were for Naxxramas, The Eye of Eternity, and The Obsidian Sanctum.

Reins of the Green Proto-Drake (Added in Patch 3.0.3)

This mount is a reward from either the Satchel of Exotic Mysteries, or from a Mysterious Egg which requires Revered reputation with The Oracles. The Egg can be bought for a mere 2g and 40s and hatches after 3 days (real time). The Egg is unique, meaning that you can only have one at a time. Wowhead puts the mount at a 5% drops chance from the Egg, and a 0.3% chance from the Satchel.

Reins of the Red Proto-Drake (Added in Patch 3.0.3)

This mount is a reward for completing Glory of the Hero, which requires you to complete all of those achievements in Heroic difficulty dungeons, this is easily done by anyone over level 80.

Reins of the Violet Proto-Drake (Added in Patch 3.2.0)

This Proto-Drake is a reward from completing the Holiday Meta Achievement, What A Long, Strange Trip It's Been. Completing this achievement will give you not only the mount, but master riding as well (if not already known.)

Reins of the Ironbound Proto-Drake (Added in Patch 3.1.3)

Rewarded to you for completing the Meta Achievement for 25-Man Ulduar, Glory of the Ulduar Raider (25 Player).

Reins of the Rusted Proto-Drake (Added in Patch 3.1.2)

This mount is awarded for finishing the Meta Achievement for 10-Man Ulduar, Glory of the Ulduar Raider (10 Player).

Reins of the Time-Lost Proto-Drake (Added in Patch 3.0.2)

The rarest of the Proto-Drakes, this guy is farmed in The Storm Peaks. He (or she, or it.) is believed to share a spawn timer with another rare in the zone, Vyragosa. One thing to note is that the mount drop is listed as 98%, this does mean that there is a very slim chance that the rare spawn MAY NOT always drop the mount. The spawn timer between the two spawns is listed anywhere from 1 hour, to several days.
Good Hunting!