Faster speed with mounts
One thing that people look forward to getting in the game is a mount. Why are they so good? Because they can save you a lot of time when you're travelling around the place. Level 40 characters can get a mount that allows them to travel 60% faster while level 60 characters can get a mount allowing them to travel 100% faster. At level 70, you can get a flying mount which can only be used in outland. Some classes like Paladins and Warlocks, can get a mount almost for free by learning a skill enabling them to summon a special mount or doing a series of quests. For eveyone else it's expensive. The mounts themselves are costly enough. 10 gold for a lvl 40 mount and 100 gold for a lvl 60 mount, though it's slightly cheaper if you buy it from a faction you have good reputation with. It's the training that's really expensive. Before you can use a lvl 40 mount you need to pay 90 gold for riding training and it's 600 gold for the lvl 60 riding training. Don't worry though, when you get to that point, the guild can help you with the cost and you'll be riding off in to the sunset.
One more note about mounts. Each faction has a mount specific to them but you can buy mounts from other factions, as long as you have reached exalted reputation with them. this makes it possible for you to have more than one mount for a character to choose from. Preview a couple of the different mounts available by clicking the links below (level 60 versions shown).