Full list of all 72 Fallout 3 achievements worth 1,550 gamerscore. It takes around 60-80 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 5 DLC packs containing 22 achievements worth 550 Gamerscore.
Completed "Galaxy News Radio"
Completed "Scientific Pursuits"
Completed "Tranquility Lane"
Completed "The Waters of Life"
Completed "Rescue from Paradise"
Completed "Take it Back!"
Completed "Those!"
Completed "Head of State"
Completed "The Replicated Man"
Completed "Blood Ties"
Completed "Strictly Business"
Completed "Stealing Independence"
Completed "Trouble on the Homefront"
Reached Level 8 with Bad Karma
Reached Level 8 with Good Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Good Karma
Reached Level 20 with Bad Karma
Killed 300 people
Killed 300 creatures
Placed a grenade or mine while pickpocketing
Made one of every custom weapon
Completed "The American Dream"
Completed "Oasis"
Discovered 100 locations
Collected 20 Vault-Tec Bobbleheads
Collected 10 Vault-Tec Bobbleheads
Completed "Following in His Footsteps"
Completed "Agatha's Song"
Completed "The Nuka-Cola Challenge"
Completed "Reilly's Rangers"
Reached Level 20 with Good Karma
Completed "You Gotta Shoot 'Em in the Head"
Completed "Tenpenny Tower"
Completed "The Superhuman Gambit"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Big Trouble in Big Town"
Picked 50 locks
Completed "The Wasteland Survival Guide"
Completed "The Power of the Atom"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Reached Level 8 with Neutral Karma
Reached Level 14 with Neutral Karma
Reached Level 20 with Neutral Karma
Won 50 Speech Challenges
Hacked 50 terminals
Kill all the Super Mutant Behemoths
Completed "Aiding the Outcasts"
Completed "The Guns of Anchorage"
Completed "Paving the Way"
Completed "Operation: Anchorage"
Completed "Free Labor"
Found All 100 Steel Ingots
Completed "Unsafe Working Conditions"
Completed "Into The Pitt"
Completed "Death From Above"
Completed "Who Dares Wins"
Completed "Shock Value"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Completed "The Local Flavor"
Discovered all locations within Point Lookout
Completed "Among the Stars"
Completed "This Galaxy Ain't Big Enough…"
Completed "Not of This World"
Collected all Alien Captive Recordings