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 "Scientific Pursuits"
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Take it Back!"
Completed "The American Dream"
Collected 20 Vault-Tec Bobbleheads
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Trouble on the Homefront"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Kill all the Super Mutant Behemoths
Collected 10 Vault-Tec Bobbleheads
Completed "Strictly Business"
Completed "Tenpenny Tower"
Completed "Big Trouble in Big Town"
Completed "Rescue from Paradise"
Completed "Agatha's Song"
Reached Level 20 with Bad Karma
Completed "You Gotta Shoot 'Em in the Head"
Completed "Reilly's Rangers"
Completed "Stealing Independence"
Made one of every custom weapon
Completed "The Replicated Man"
Won 50 Speech Challenges
Completed "Head of State"
Hacked 50 terminals
Discovered 100 locations
Completed "The Nuka-Cola Challenge"
Reached Level 20 with Good Karma
Reached Level 20 with Neutral Karma
Completed "Oasis"
Completed "The Superhuman Gambit"
Killed 300 creatures
Killed 300 people
Reached Level 14 with Neutral Karma
Reached Level 14 with Bad Karma
Completed "Those!"
Reached Level 14 with Good Karma
Completed "Blood Ties"
Picked 50 locks
Placed a grenade or mine while pickpocketing
Reached Level 8 with Bad Karma
Reached Level 8 with Neutral Karma
Reached Level 8 with Good Karma
Completed "The Wasteland Survival Guide"
Completed "The Power of the Atom"
Completed "Escape!"
Took the G.O.A.T.
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
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Discovered all locations within Point Lookout
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"