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