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"
Completed "Tenpenny Tower"
Completed "Strictly Business"
Completed "Reilly's Rangers"
Kill all the Super Mutant Behemoths
Placed a grenade or mine while pickpocketing
Completed "The Wasteland Survival Guide"
Completed "Stealing Independence"
Reached Level 8 with Good Karma
Reached Level 8 with Neutral Karma
Completed "Those!"
Killed 300 people
Completed "Agatha's Song"
Picked 50 locks
Discovered 100 locations
Completed "Oasis"
Completed "Head of State"
Completed "Blood Ties"
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Reached Level 20 with Good Karma
Completed "Picking up the Trail"
Completed "Big Trouble in Big Town"
Completed "Trouble on the Homefront"
Completed "The Waters of Life"
Completed "The Superhuman Gambit"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Galaxy News Radio"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 14 with Good Karma
Completed "The Replicated Man"
Completed "Following in His Footsteps"
Completed "The Power of the Atom"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Completed "The Nuka-Cola Challenge"
Reached Level 8 with Bad 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 creatures
Won 50 Speech Challenges
Hacked 50 terminals
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 "Free Labor"
Completed "Unsafe Working Conditions"
Completed "Into The Pitt"
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