Ashes of Al'ar

Ashes of Al'ar

The mount Ashes of Al'ar is a rare drop from the raid boss Kael'thas Sunstrider in Tempest Keep. (The drop rate is 2.0%.) Tempest Keep is located in Netherstorm, Outland. This raid is reasonably easy to solo by any level 90-100 class and there is no option to choose 10/25 player normal/heroic as it is just 25 player normal. It is not necessary to kill the other bosses, however they have a chance to drop rare pets. Getting the mount also rewards the feat of strength [Ashes of Al'ar]

Green Proto-Drake

Green Proto-Drake

The green Proto-Drake is a low drop chance from [Mysterious Egg] which is bought from Geen, the Oracles quartermaster in Scholozar Basin, Northrend. To purchase the egg you are required to be revered with the Oracles faction, this will not take long and is done through doing daily quests for them. However be aware that if you quested in this area when levelling that you may have chosen to go with the Frenzyheart Tribe instead of the Oracles - if you did not level in this area then there will be a short quest line to complete. [The Part-time Hunter] is the first quest in the chain. 

Cenarion War Hippogryph

Cenarion War Hippogryph

This hippogryph mount can be obtained through being exalted with the Cenarion Expedition. You can either complete dailies for this faction or run through appropriate dungeons. Personally I would recommend the dungeons in Coilfang Reservoir if you choose to do it this way which is located in Zangarmarsh, Outland.

Grove Warden

Grove Warden

This mount can currently be obtained through killing Archimonde in Hellfire Citadel on heroic mode or higher. He will drop a quest item that will direct you to Moonglade and then you will be rewarded this mount. It can be challenging to find a group for this if you do not raid and the item level requirement is around 700+ and people often look for experience such as Ahead of The Curve: The Black Gate or Time is a Flat Circle. However you could always pay gold to a guild for a boost if you have the gold or slowly build up your item level and hope to find a group not looking for previous experience.

Argent Tournament

The Argent Tournament has a variety of different mounts to earn and can be a fairly long grind. To obtain them you will need to complete quests for the Argent Tournament which is located North East in Icecrown. You will eventually begin to earn Champion's Seals from completing dailies which is what you will need to purchase the mounts. Some will require you to be exalted with a specific faction (race factions) or Sunreavers (horde) depending on which mount it is.

Here are two that I have collected:

Sunreaver Dragonhawk
Requires Sunreavers - Exalted
Costs 100 Champion's Seals

Argent Hippogryph
Costs 150 Champion's Seals

The Headless Horseman's Mount

The Headless Horseman's Mount

This mount is a 0.5% drop from Loot-Filled Pumpkin which is obtainable from doing the special event dungeon during Hallow's End which is accessible through the dungeon finder. You can only get the Loot-Filled pumpkin once per day per character, so if you have alts then you may get it more than once a day for a higher chance at getting it.

Red Drake

The red drake can be obtained through exalted reputation with Wyrmrest Accord. You can either buy a tabard from them and run through Cataclysm dungeons or you could purchase reputation badges with the new currency from timewalking dungeons. The commendation badges for the Wyrmrest Accord may only be purchased from the timewalking dungeon vendor in Dalaran.