Standard heal potions are usually on the same timer (2 min), allowing you to use only one per fight. There are however a few other consumable heal items that are on different timers (and those are only 1 min). That comes in especially helpful in PvP encounters.
In Felwood there is a repeatable quest that allows you to get several rewards, including +10 STA food, a one hour buff (+5% chance to land a critical hit and +15 to all attributes) and, exactly, two heal items, each of them on a different timer and both of them not on the standard heal potion timer.
First you will have to do the Cleansing Felwood quest (min lvl 4: http://www.thottbot.com/?q=1087
After that a new quest line opens up, that allows you to get "Cenarion Plant Salve": http://www.thottbot.com/?s=salve+via
The salve can be applied to the corrupted plants in Felwood to get the above stated rewards. The plants that yield the heal potions are:
Corrupted Night Dragon (394 - 456 hp heal potion) Locations: http://www.thottbot.com/?m=66899
Corrupted Whipper Root (700 - 900 hp heal potion) Locations: http://www.thottbot.com/?m=66899
Since those quests are repeatable and Cenarion Plant Salve can be gained from pretty much anything you do in Felwood, it's a reliable source.