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