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.
Got the Pip-Boy 3000
Took the G.O.A.T.
Completed "Escape!"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "Finding the Garden of Eden"
Completed "The American Dream"
Completed "Take it Back!"
Completed "The Power of the Atom"
Reached Level 14 with Neutral Karma
Reached Level 14 with Good Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Reached Level 20 with Good Karma
Won 50 Speech Challenges
Reached Level 8 with Neutral Karma
Reached Level 8 with Good Karma
Placed a grenade or mine while pickpocketing
Kill all the Super Mutant Behemoths
Collected 20 Vault-Tec Bobbleheads
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Made one of every custom weapon
Killed 300 people
Discovered 100 locations
Completed "Oasis"
Completed "Agatha's Song"
Collected 10 Vault-Tec Bobbleheads
Completed "The Nuka-Cola Challenge"
Completed "Trouble on the Homefront"
Completed "Strictly Business"
Completed "Big Trouble in Big Town"
Hacked 50 terminals
Completed "The Superhuman Gambit"
Completed "The Waters of Life"
Completed "Reilly's Rangers"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "Head of State"
Reached Level 14 with Bad Karma
Completed "Tenpenny Tower"
Completed "You Gotta Shoot 'Em in the Head"
Killed 300 creatures
Completed "The Replicated Man"
Completed "The Wasteland Survival Guide"
Completed "Stealing Independence"
Picked 50 locks
Completed "Those!"
Reached Level 8 with Bad Karma
Completed "Blood Ties"
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 Good Karma
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
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"