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