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