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 "Following in His Footsteps"
Hacked 50 terminals
Won 50 Speech Challenges
Completed "Take it Back!"
Completed "Strictly Business"
Killed 300 people
Discovered 100 locations
Made one of every custom weapon
Completed "Head of State"
Reached Level 20 with Good Karma
Placed a grenade or mine while pickpocketing
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Completed "You Gotta Shoot 'Em in the Head"
Completed "Reilly's Rangers"
Completed "Agatha's Song"
Completed "Trouble on the Homefront"
Completed "Blood Ties"
Collected 20 Vault-Tec Bobbleheads
Collected 10 Vault-Tec Bobbleheads
Kill all the Super Mutant Behemoths
Reached Level 14 with Bad Karma
Reached Level 14 with Neutral Karma
Reached Level 8 with Neutral Karma
Reached Level 8 with Bad Karma
Completed "Stealing Independence"
Picked 50 locks
Completed "Oasis"
Completed "The Replicated Man"
Completed "The Nuka-Cola Challenge"
Killed 300 creatures
Completed "Those!"
Completed "The Superhuman Gambit"
Completed "Big Trouble in Big Town"
Completed "The American Dream"
Reached Level 14 with Good Karma
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "Tenpenny Tower"
Completed "The Power of the Atom"
Completed "The Wasteland Survival Guide"
Reached Level 8 with Good Karma
Completed "Galaxy News Radio"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Completed "Aiding the Outcasts"
Completed "The Guns of Anchorage"
Completed "Paving the Way"
Completed "Operation: Anchorage"
Completed "Free Labor"
Completed "Unsafe Working Conditions"
Found All 100 Steel Ingots
Completed "Into The Pitt"
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Reached Level 30 with Bad 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
Completed "This Galaxy Ain't Big Enough…"
Collected all Alien Captive Recordings
Completed "Among the Stars"
Completed "Not of This World"