Apprentice Riding

As of patch 3.2

Apprentice Riding (Skill 75)

o 60% land mount speed
o Requires level 20
o Cost: 4 gold
o Mount cost: 1 gold
o Mail will be sent to players at level 20 guiding them to the riding trainer

Journeyman Riding (Skill 150)

o 100% land mount speed
o Requires level 40
o Cost: 50 gold
o Mount cost: 10 gold
o Mail will be sent to players at level 40 guiding them back to the riding trainer

Expert Riding (Skill 225)

o 150% flying mount speed; 60% land mount speed
o Requires level 60
o Cost: 250 gold (faction discounts now apply: Honor Hold [Alliance]; Thrallmar [Horde])
o Mount Cost: 50 gold
o Can now be learned in Honor Hold (Alliance) or Thrallmar (Horde)

Artisan Riding (Skill 300)

o 280% flying mount speed; 100% land mount speed
o Requires level 70
o Cost: 5,000 gold (faction discounts now apply: Honor Hold or Valiance Expedition [Alliance]; Thrallmar or Warsong Offensive [Horde])
o Mount Cost: 100 gold

Faction discounts apply to all mount types now.

Friendly = 5% discount
Honored = 10% discount
Revered = 15% discount
Exalted = 20% discount

No, you must buy your Apprentice Riding Skill in order to get every other riding skill (including flying).
Apprentice Riding (60%) -> Journeyman Riding (100%) -> Expert Riding (60% Flying) -> Artisan Riding (280% Flying, 100% Land)

A druid needs to buy Apprentice and Journeyman Riding skill to get Expert riding skill for free.