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