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