Full list of all 80 Borderlands achievements worth 1,750 gamerscore. It takes around 40-50 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 30 achievements worth 750 Gamerscore.
Completed all missions in the Rust Commons
Completed 15 missions in co-op
Rescued enough Claptraps to earn 42 inventory slots
Raced around the Ludicrous Speedway in record time
Killed the Vault Boss
Killed Flynt
Completed all missions in the Arid Badlands
Discovered Crimson Lance Enclave
Killed 25 enemies with incendiary weapons
Killed 25 enemies with corrosive weapons
Killed an enemy with the Siren's action skill
Killed an enemy plumber-style
Mastered the technology of Pandora
Emerged victorious from an arena match
Killed Krom
Discovered Krom's Canyon
Killed 15 enemies with the Hunter's action skill
Sold 50 guns to a shop
Earned level 50
Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Killed the Rakk Hive
Discovered Trash Coast
Applied an elemental artifact
Killed 15 enemies with the Berserker's action skill
I bet you never thought you'd be here.
Completed 5 missions in the Rust Commons
Killed 15 enemies with the Soldier's action skill
Discovered The Scrapyard
Equipped a class mod for your character
Killed Sledge
Killed 25 enemies with shock weapons
Discovered Headstone Mine
Killed 25 enemies with explosive weapons
Discovered Sledge's Safe House
Killed 5 Rakk in under 10 seconds
Killed 25 enemies by ramming them with any vehicle
Earned level 40
Rescued a groupmate from death in a co-op game
Won a duel against another player
Won a duel without taking damage
Earned $1,000,000
Earned level 30
Earned level 20
Reached proficiency level 10 with any weapon type
Earned level 10
Discovered Eridian Promontory
Gamed with fame
Earned level 5
Discovered Skag Gully
Completed 5 missions in the Arid Badlands
Completed the "Braaaaaaaaaaaaains!" mission
Killed Ned. Again.
Killed Ned...sort of
Completed the "Jakobs Fodder" mission
Completed the "House of the Ned" mission
Reached the end of the larger challenge in the Hell-Burbia coliseum
Reached the end of each of the 3 larger challenges with one character
Reached the end of the larger challenge in The Angelic Ruins coliseum
Reached the end of the larger challenge in The Gully coliseum
Completed the Prove Yourself mission
Completed all missions in Secret Armory
Killed each of the loot midgets
Reached Level 61
Paid for a worthless tour of the world's largest bullet
Killed Crawmerax the Invincible
Destroyed the Lance Depot
Rescued Athena
Destroyed a Lancer while in a Racer
Built the New Car: Monster
Reached Level 51
Collected 3 panties, 5 fish in a bag, and 15 pizzas
Collected 15 Claptrap bobbleheads
Found 25 Claptrap oil cans
Read all 6 Claptrap statue placards
Completed Tannis' crazy request
Defeated the Interplanetary Ninja Assassin Claptrap
The Commandant is dead-trap
Killed Ned...again and again and again
Knoxx is at rest...finally
Collected 5 3D glasses