Five Exalted Reputations

Some of the easiest reputations to earn are also the ones that will benefit you the most. Exalted with EACH of the racial factions. What is also nice about these is they have the added benefit of giving you another achievement and a Title. Ambassador of the Alliance or Ambassador of the Horde respectively. The way you gain these reputations is basically the same for all 10 factions.
Go to the races starting area and do ALL the quests there.

Now I am going to run with the assumption in this series that you are a level 80 but where it applies I will make note if a reputation can be easily earned by someone LOWER than that. Since these ALL start at level 1 ANYONE can participate in gaining this reputation achievement. In addition to this there are several repeatable and seasonal quests that ALSO give racial faction reputations.

Ambassador of the Alliance requires you to reach exalted reputation with Darnassus, Exodar, Gnomeregan, Ironforge, and Stormwind. While none of these factions have quartermasters associated with them that will allow you to gain other items however they DO control the majority of the Alliance flight paths and shops. This means that you get a DISCOUNT at these sites which in the end can save you a GREAT deal of money.

Danassus has 759 quests that gives faction reputation.
Exodar has 865 quests that give faction reputation.
Gnomeregan Exiles has 855 quests that give faction reputation.
Iornforge has 761 quests that give faction reputation.
Stormwind has 716 quests that give faction reputation.

Ambassador of the Horde requires that you reach exalted reputation with Darkspear Tolls, Orgrimmar, Silvermoon City, Thunder Bluff and Undercity. Now the Horde have a DISTINCT disadvantage here in that there are FEWER quests that provide reputation over all for the Horde racial factions. This means you really can't skip any if you wish to do this achievement. In addition these factions also control a great many of the fight paths and shops so again this means DISCOUNTS!!

Darkspear Trolls has 572 quests that give faction reputation.
Orgrimmar has 522 quests for their faction reputation.
Silvermoon City has 649 quests for their faction reputation.
Thunder Bluff has 563 quests for their faction reputation.
Undercity has 520 quests for their faction reputation.

A few other "Tricks" for doing these reputations if you (Like me) leveled back when reputation gains were MUCH lower for the racial factions. Doing ALL the quests and getting to level 60 would get you to ALMOST revered at that time so you really only had two options. You could farm cloth and do the repeatable Runecloth turn ins. OR you could also farm reputation by Pvping in Alterac Valley. Doing the turns in there is how many of us reached Exalted with the Exodar and Silvermoon City factions EVEN BEFORE Burning Crusade was released. A third option has now becoming available in the form of the Argent Tournament. Here (once you reach Champion Rank) you may choose to get a Champion's Writ which can then be turned in for commendation badges from your desired faction.

Happy Questing!