To get into vault city's vault without being a citizen all you have to do is get directly in front of the vault right before the gaurds say "only citizens allowed" then go into combat mode, enter the vault and WHA-LA! Free access
In the NCR go to the place where the girl asked you to help talk the cop out of suicide and repair the computer.
Talk to the girl and you will get 4000exp, a first aid kit and a science book.
Repair the computer again and talk to her again and the same will happen.
To hear comments by the development team, hold [Shift] during the credits.
Unlimited Money And Jet
In the Den, there is a thug named Joey. He will try to sell you the drug "Jet".
Talk to him and he'll ask you for $500 a dose. When you first talk to him, have less than $500 in your inventory and say you'll buy it. He will say you don't have enough money and tell you not to buy it anywhere else.
There will be an option that says "Wait, I'll buy it". Click on that and he'll say "You'll be coming back".
Then say "Maybe". In your inventory, you will have the jet, without even paying for it. Here comes the best part!
Go into his inventory by using the steal skill. He will have the $500 you were supposed to give him.
You can then steal that money! You may do this as many times you wish for unlimited money and jet.