Topic City Reputation
87 Tauren Death Knight
1) Fast and cheap, do the starter area quests for each city. If you do the Durotar orc/troll starter quests, you will get rep for both Orgrimmar and Darkspear at the same time. Same goes for Undercity (Deathknell) and Thunder Bluff (Red Cloud Mesa).
2) Do the argent tournament dailies. The 4 valiant quests will give 1000 rep to the city you represent and 250 for each other city. The champion quests offer the Champion's writ, which you can turn in for 250 rep (and 62.5 rep for other cities).
Go to wowhead.com and look up those reputations. Their rep pages will give a list of quests that up your reputation.