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