The lights are on
1. You definitely want the Terrible Shotgun. This can be found carried by a raider named smiling Jack in the bottom end of evergreen mills (place with super mutant behemoth) ....he doesn't attack you and tries to sell you stuff, you can kill him without losing karma and take it.
2. The Lincolns Repeater is the best rifle you can get. This can be found in a case sitting in a room up the stairs in the museum of history at the mall, instead of entering the town of Ghouls when you enter the museum take the other door.
3. The alien blaster is pretty much the best weapon you can get. (Other than the Novasurge in the Mothership Zeta Add-On) To get this you head north of the MDPL-13 Power Station until you stumble on an alien UFO crash site, around the ship will like the dead body of an alien captain who has the Blaster and 120 ammo.
4. The Mauler...you can just tell by it's name. In The Pitt Add-on you must collect 80 steel ingots and give them to Everett and he will give you it as a reward.
5. Paulsons Revolver, the ONLY NON SCOPED .44!!! When on Mothership Zeta you can kill Paulson and take it from him without any loss of karma and the other characters won't attack you. I recommend waiting until the mission ends...he's one of the most epic characters...and remember that once you exit the ship he's gone forever.
6. Blackhawk...oh yeah. Go to the residence of a lady named Agatha, west of the scrapyard and complete the quest Agatha's song, remember in the speech options you must ASK her for a reward.
7. Gauss Rifle (operation Anchorage) is literally one of the strongest energy weapons in the game is scoped with one shot that can knock over an albino rad scorpion!