Fallout 3 karma achievements and trophies

 are achievements and trophies which require you to have either bad, neutral or good karma upon reaching levels 8, 14 and 20.

Good Karma

 * Protector (level 8)
 * Ambassador of Peace (level 14)
 * Last, Best Hope of Humanity (level 20)

Neutral Karma

 * Mercenary (level 8)
 * Pinnacle of Survival (level 14)
 * Paradigm of Humanity (level 20)

Bad Karma

 * Reaver (level 8)
 * Harbinger of War (level 14)
 * Scourge of Humanity (level 20)

Strategies

 * An easy way to do this is continue the game as an evil person save at levels 7, 12, 18 (has to be near leveling up) and then when you re-load you just keep donating caps to the church in the game until desired karma level (If you don't have enough caps to raise your karma enough just sell all your stuff since it's not your main character). Then do anything to level up (for 12 and 18 just use the Here and Now perk to instantly raise your level when you reach 13 or 19). You can use the caps method to elevate your karma and simply execute one high exp rivet city guard, like the one standing out front to push yourself over the leveling line.
 * Another way is to play through as a good player and then when your getting to a level for the award just head to megaton and start a killing spree until desired karma level (Remember to save and re-load).
 * Massacring rivet city can be more effective depending, it may be a tougher fight, but the guards give 50 points of experience per kill vs the measly amount given by megaton individuals. It may be a choice better for players further from their actual level up.
 * Also you could play as a neutral character and not complete the The Power of Atom Quest and then easily blow up or save Megaton with/from the bomb.
 * You can also make use of the here and now perk, as it can take you 2 levels in one level-up. If you have a save game at say late level 12, and not at 13, then modifying your karma and then leveling up from there with the perk will get you the achievements.