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