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.
Reached Level 8 with Good Karma
Reached Level 14 with Bad Karma
Made one of every custom weapon
Collected 20 Vault-Tec Bobbleheads
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Reached Level 14 with Neutral Karma
Won 50 Speech Challenges
Hacked 50 terminals
Picked 50 locks
Reached Level 8 with Bad Karma
Kill all the Super Mutant Behemoths
Collected 10 Vault-Tec Bobbleheads
Completed "The Nuka-Cola Challenge"
Completed "The Superhuman Gambit"
Completed "Strictly Business"
Completed "Blood Ties"
Completed "Head of State"
Reached Level 20 with Good Karma
Completed "Oasis"
Discovered 100 locations
Completed "The Wasteland Survival Guide"
Completed "Stealing Independence"
Completed "Those!"
Completed "You Gotta Shoot 'Em in the Head"
Killed 300 people
Completed "Reilly's Rangers"
Completed "Agatha's Song"
Completed "Tenpenny Tower"
Killed 300 creatures
Completed "Big Trouble in Big Town"
Reached Level 14 with Good Karma
Completed "The Replicated Man"
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "Trouble on the Homefront"
Completed "The Waters of Life"
Reached Level 8 with Neutral Karma
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
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"
Found All 100 Steel Ingots
Completed "Free Labor"
Completed "Unsafe Working Conditions"
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"
Discovered all locations within Point Lookout
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Completed "The Local Flavor"
Collected all Alien Captive Recordings
Completed "This Galaxy Ain't Big Enough…"
Completed "Among the Stars"
Completed "Not of This World"