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
Made one of every custom weapon
Kill all the Super Mutant Behemoths
Discovered 100 locations
Killed 300 people
Completed "Scientific Pursuits"
Completed "Tranquility Lane"
Completed "The Wasteland Survival Guide"
Completed "Those!"
Completed "Blood Ties"
Completed "The Power of the Atom"
Killed 300 creatures
Completed "Oasis"
Reached Level 8 with Neutral Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Neutral Karma
Collected 10 Vault-Tec Bobbleheads
Reached Level 20 with Neutral Karma
Reached Level 20 with Bad Karma
Hacked 50 terminals
Won 50 Speech Challenges
Reached Level 8 with Bad Karma
Completed "Strictly Business"
Completed "Reilly's Rangers"
Completed "The Nuka-Cola Challenge"
Reached Level 20 with Good Karma
Completed "You Gotta Shoot 'Em in the Head"
Completed "Head of State"
Completed "The Superhuman Gambit"
Completed "Agatha's Song"
Completed "Tenpenny Tower"
Completed "Big Trouble in Big Town"
Completed "Stealing Independence"
Picked 50 locks
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Reached Level 14 with Good Karma
Completed "Trouble on the Homefront"
Completed "The Waters of Life"
Completed "The Replicated Man"
Reached Level 8 with Good Karma
Placed a grenade or mine while pickpocketing
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Completed "Aiding the Outcasts"
Completed "The Guns of Anchorage"
Completed "Paving the Way"
Completed "Operation: Anchorage"
Completed "Free Labor"
Completed "Unsafe Working Conditions"
Found All 100 Steel Ingots
Completed "Into The Pitt"
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Reached Level 30 with Good Karma
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Discovered all locations within Point Lookout
Completed "The Local Flavor"
Completed "Walking With Spirits"
Completed "A Meeting of the Minds"
Collected all Alien Captive Recordings
Completed "Not of This World"
Completed "Among the Stars"
Completed "This Galaxy Ain't Big Enough…"