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