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
Collected 20 Vault-Tec Bobbleheads
Completed "Strictly Business"
Picked 50 locks
Made one of every custom weapon
Discovered 100 locations
Killed 300 people
Collected 10 Vault-Tec Bobbleheads
Completed "The Nuka-Cola Challenge"
Kill all the Super Mutant Behemoths
Completed "Big Trouble in Big Town"
Placed a grenade or mine while pickpocketing
Completed "The Superhuman Gambit"
Completed "Rescue from Paradise"
Completed "Head of State"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Agatha's Song"
Completed "Tenpenny Tower"
Reached Level 8 with Bad Karma
Reached Level 8 with Neutral Karma
Won 50 Speech Challenges
Completed "Reilly's Rangers"
Completed "Take it Back!"
Reached Level 20 with Good Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Trouble on the Homefront"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "The Replicated Man"
Completed "Galaxy News Radio"
Completed "Stealing Independence"
Reached Level 14 with Good Karma
Reached Level 14 with Neutral Karma
Reached Level 14 with Bad Karma
Completed "Blood Ties"
Completed "Following in His Footsteps"
Completed "Those!"
Completed "The Wasteland Survival Guide"
Killed 300 creatures
Completed "Oasis"
Reached Level 8 with Good Karma
Completed "The Power of the Atom"
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 Bad Karma
Reached Level 30 with Neutral Karma
Completed "Who Dares Wins"
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
Collected all Alien Captive Recordings
Completed "This Galaxy Ain't Big Enough…"
Completed "Among the Stars"
Completed "Not of This World"