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