By the bonfire behind the hidden wall in Darkroot garden is a locked door sealed by the Astoras crest (which you can purchase for 20,000 souls at the Blacksmith in the undead parish). It creates a shortcut to the boss Sif. However, before that is a mage, a semi-invisible knight, rogue, and an archer. You can go down the staircase just outside of the door and see the mage standing by a lightplant. With a bow and one well placed arrow(doesn't matter what type, the key is to hit him, not kill him) you can shoot him once and then lure him back into the area by the bonfire. He's very easy to kill alone, but make sure the semi-invisible knight doesn't follow him. Kill the mage and you will get 2000 souls. Now here's the kicker; every time you rest at the bonfire, he returns to life. Rinse and repeat to accumulate great amounts of souls in a short period of time.