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