At the beginning of the Southpaw Steam & Power Facility, where you do the "Assassinate The Assassins" mission, is a room of lockers and small boxes. Check all the boxes and lockers, then go to the "Pause" menu. Select "Quit", then "Save And Quit". When the game returns to the title screen, continue your game. You will appear at the begging of Southpaw, and the boxes and lockers will have respawned with new items (weapons, money, ammo, shields, and Eridium). Loot the boxes and lockers again and repeat. The entire process is very fast and you can receive at least one Eridium every four times that the room is cleared. This is a good way to get black market items early in the game.