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