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