Inferno/Act 1/Legacy of Cain
When you find Adria's hut, go down into the cellar and clear out Captain Doltyn and his gang. The big cauldron in the middle always drops a health potion -- a Mythic one in Inferno. Grab it, exit the game, and resume to another game. You should respawn right there and the Cauldron has its state reset so you can pop another potion. You can continue to do this as long as you want.

If you want to run your own macro, you can easily do it with a program called AutoYou