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