Infinite Souls One
There are a couple of hidden cheats in "Darksiders" that give you infinite souls. The first is located in Chapter Four on the level "The Iron Canopy, Broodmother." During the final battle with the Broodmother, you can obtain souls by tossing her eggs sacs against the ceiling. Kill the Broodmother as quickly as possible, but do not leave her lair as the egg sacs will keep respawning, allowing you to gather as many souls as you wish.
Infinite Souls Two
The second infinite souls cheat is found in Chapter Five on the level "The Black Throne, The Third Guardian III." After you cross the bridge with spinning portals you will be attacked by the Shield Lord and four soldiers. Leave the Shield Lord alive and focus your attacks on the soldiers. Each time you kill a soldier, he will leave behind a soul. However, because the soldiers reappear every time they die, you can keep on collecting souls until you decide to kill the Shield Lord.
Unlock the Harvester Weapon
A giant scythe, the Harvester is a powerful weapon that causes deadly damage to your enemies. You can unlock this weapon by pausing the game and going to the "Enter Code" heading under the "Game Options" menu. Enter the code: "The Hollow Lord" and the Harvester is now available to buy from Vulgrim for 1,000 souls.
Boost The Chaoseater Blade
On the final level of Chapter Three -- "Ashlands, The Stygian" -- you can max out the very useful Chaoseater Blade by attacking it over and over again. Kill the phantom soldiers first and then attack the Stygian by riding alongside it, but do not hit the creature's helmet or it will attack. Use Combat Lore to boost the experience from each attack and when the Stygian disappears under the sand and resurfaces, repeat the same attack strategy until the Chaoseater Blade is maxed out.