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.
Reached Level 8 with Bad Karma
Reached Level 8 with Neutral Karma
Reached Level 14 with Bad Karma
Won 50 Speech Challenges
Reached Level 14 with Neutral Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Killed 300 people
Completed "Take it Back!"
Completed "The American Dream"
Completed "The Nuka-Cola Challenge"
Discovered 100 locations
Kill all the Super Mutant Behemoths
Made one of every custom weapon
Hacked 50 terminals
Collected 20 Vault-Tec Bobbleheads
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Reached Level 20 with Good Karma
Completed "Agatha's Song"
Completed "Oasis"
Completed "Rescue from Paradise"
Completed "Strictly Business"
Completed "Big Trouble in Big Town"
Collected 10 Vault-Tec Bobbleheads
Completed "You Gotta Shoot 'Em in the Head"
Completed "Head of State"
Completed "Tenpenny Tower"
Completed "Reilly's Rangers"
Killed 300 creatures
Completed "Trouble on the Homefront"
Completed "The Superhuman Gambit"
Reached Level 14 with Good Karma
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "The Replicated Man"
Completed "The Wasteland Survival Guide"
Placed a grenade or mine while pickpocketing
Picked 50 locks
Completed "Those!"
Completed "Stealing Independence"
Reached Level 8 with Good Karma
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Blood Ties"
Completed "The Power of the Atom"
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"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "Death From Above"
Completed "Who Dares Wins"
Completed "Shock Value"
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"