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