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