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.
Hacked 50 terminals
Won 50 Speech Challenges
Discovered 100 locations
Kill all the Super Mutant Behemoths
Killed 300 people
Made one of every custom weapon
Completed "Trouble on the Homefront"
Completed "The Nuka-Cola Challenge"
Reached Level 20 with Good Karma
Collected 20 Vault-Tec Bobbleheads
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Neutral Karma
Completed "Agatha's Song"
Picked 50 locks
Completed "Reilly's Rangers"
Completed "You Gotta Shoot 'Em in the Head"
Collected 10 Vault-Tec Bobbleheads
Completed "Oasis"
Completed "Head of State"
Completed "Those!"
Completed "The Superhuman Gambit"
Completed "Rescue from Paradise"
Completed "Strictly Business"
Completed "Tenpenny Tower"
Killed 300 creatures
Reached Level 14 with Good Karma
Placed a grenade or mine while pickpocketing
Completed "Big Trouble in Big Town"
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Stealing Independence"
Completed "The Wasteland Survival Guide"
Reached Level 8 with Bad Karma
Reached Level 8 with Neutral Karma
Completed "The Waters of Life"
Completed "The Replicated Man"
Completed "Tranquility Lane"
Reached Level 8 with Good Karma
Completed "Scientific Pursuits"
Completed "Blood Ties"
Completed "Galaxy News Radio"
Completed "The Power of the Atom"
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"
Completed "Free Labor"
Completed "Unsafe Working Conditions"
Found All 100 Steel Ingots
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good 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"