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