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