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