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