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.
Got the Pip-Boy 3000
Took the G.O.A.T.
Completed "Escape!"
Completed "Big Trouble in Big Town"
Completed "Head of State"
Completed "Oasis"
Completed "Agatha's Song"
Reached Level 14 with Neutral Karma
Reached Level 14 with Good Karma
Killed 300 creatures
Picked 50 locks
Completed "Rescue from Paradise"
Killed 300 people
Completed "Take it Back!"
Completed "The American Dream"
Kill all the Super Mutant Behemoths
Hacked 50 terminals
Discovered 100 locations
Made one of every custom weapon
Completed "The Nuka-Cola Challenge"
Collected 20 Vault-Tec Bobbleheads
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Won 50 Speech Challenges
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Reached Level 20 with Good Karma
Completed "Strictly Business"
Collected 10 Vault-Tec Bobbleheads
Completed "The Superhuman Gambit"
Completed "Blood Ties"
Reached Level 8 with Good Karma
Reached Level 8 with Bad Karma
Completed "Those!"
Completed "Reilly's Rangers"
Reached Level 14 with Bad Karma
Completed "You Gotta Shoot 'Em in the Head"
Completed "Stealing Independence"
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Trouble on the Homefront"
Completed "Tenpenny Tower"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Reached Level 8 with Neutral Karma
Completed "Scientific Pursuits"
Completed "The Replicated Man"
Completed "The Wasteland Survival Guide"
Placed a grenade or mine while pickpocketing
Completed "The Power of the Atom"
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"
Completed "Shock Value"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "Who Dares Wins"
Completed "Death From Above"
Discovered all locations within Point Lookout
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
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"