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 "Take it Back!"
Completed "Big Trouble in Big Town"
Completed "Head of State"
Completed "Stealing Independence"
Made one of every custom weapon
Killed 300 people
Killed 300 creatures
Discovered 100 locations
Collected 20 Vault-Tec Bobbleheads
Hacked 50 terminals
Reached Level 20 with Neutral Karma
Reached Level 20 with Good Karma
Won 50 Speech Challenges
Collected 10 Vault-Tec Bobbleheads
Completed "The Nuka-Cola Challenge"
Reached Level 14 with Good Karma
Reached Level 14 with Neutral Karma
Reached Level 8 with Neutral Karma
Reached Level 8 with Good Karma
Completed "Agatha's Song"
Completed "The American Dream"
Kill all the Super Mutant Behemoths
Completed "Trouble on the Homefront"
Completed "Oasis"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 20 with Bad Karma
Completed "Those!"
Completed "The Superhuman Gambit"
Completed "Reilly's Rangers"
Completed "Galaxy News Radio"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Following in His Footsteps"
Reached Level 14 with Bad Karma
Completed "Rescue from Paradise"
Completed "Strictly Business"
Completed "Blood Ties"
Completed "Tenpenny Tower"
Completed "The Wasteland Survival Guide"
Picked 50 locks
Completed "The Replicated Man"
Reached Level 8 with Bad Karma
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"
Found All 100 Steel Ingots
Completed "Unsafe Working Conditions"
Completed "Into The Pitt"
Completed "Death From Above"
Completed "Shock Value"
Completed "Who Dares Wins"
Reached Level 30 with Good Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Bad Karma
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Discovered all locations within Point Lookout
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"