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