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