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