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