Title Reward: of the Undercity

1. Wowhead has a list of all the quests you can complete as well as how much reputation you will gain from each one.
2. If questing is not your thing, you can always donate cloth for reputation. Visit Ralston Farnsley in Undercity (The Magic Quarter 71, 29) to turn in cloth. Level 12+ A Donation of Wool, Level 26+ A Donation of Silk, Level 50+ A Donation of Runecloth and Level 40+ A Donation of Mageweave. Each donation of 60 cloths will give you 350 reputation.
3. Complete A Threat from Above, Taking Battle to the Enemy and/or The Grand Melee after gaining Champion status with one of your faction's cities. You'll be able to choose a Commendation Badge for the city of your choosing that will give you 250 reputation.