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