Infinite Money:
First find a piece of unrefined ore usally from Merchants around Broken Hills. Then go to where Marcus is standing and head down until you find an office with a Ghoul inside. Talk to him and tell him to refine the ore. He'll charge you a wee bit to refine it, say Yes. He should tell you to come back in a day. Press Z to access the PIP Boy sleep function, and select 24hrs after this time (eg. If you do this at 8am exactly, tell the PIP boy to rest until morning 8am). Now he'll have refined the ore. He suggest that you leave the ore with him and he'll give you 1500 extra if you say yes. Say yes, then say thanks. Talk to him again and he'll ask you again if you want leave the ore with him and he'll give you 1500 again. You can repeat this over and over again no matter how much ore you have.
*Note: It is best to rest untill morning, then give him the ore.

Easy Money:
Find the casino in on of the towns and save the game, then gamble. If you win, save the game and play agan. If you loose, load the game so you have no record of ever loosing that money.

Massacre:
In NCR there is a scientist that will ask you to test this new drug on a mutant. He will say that there are some mutants in broken hills, don't go to broken hills but go to the military base and use the drug on one of the mutants. Then go back and say you used the drug you will get a cyber dog thats got crap attack and cant carry anything, and 1000 experiance talk to him again and he will give you the same drug again. you can do this until you have wiped out all the mutants in the game.