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