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