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