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.
Emerged victorious from an arena match
Won a duel against another player
Rescued a groupmate from death in a co-op game
Completed 15 missions in co-op
Reached proficiency level 10 with any weapon type
Killed 25 enemies with corrosive weapons
Killed 25 enemies with shock weapons
Killed 25 enemies with incendiary weapons
Killed 25 enemies with explosive weapons
Equipped a class mod for your character
Killed an enemy with the Siren's action skill
Killed 15 enemies with the Hunter's action skill
Completed 5 missions in the Arid Badlands
Completed all missions in the Arid Badlands
Completed 5 missions in the Rust Commons
Completed all missions in the Rust Commons
Killed an enemy plumber-style
Mastered the technology of Pandora
Killed Sledge
Killed Krom
Killed Flynt
Killed the Rakk Hive
Killed the Vault Boss
Applied an elemental artifact
Earned level 5
Earned level 10
Earned level 20
Earned level 30
Earned level 40
Discovered Skag Gully
Discovered Sledge's Safe House
Discovered Headstone Mine
Discovered Trash Coast
Discovered The Scrapyard
Discovered Krom's Canyon
Discovered Crimson Lance Enclave
Discovered Eridian Promontory
Earned level 50
Killed 25 enemies by ramming them with any vehicle
Killed 5 Rakk in under 10 seconds
Earned $1,000,000
Sold 50 guns to a shop
Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Won a duel without taking damage
Killed 15 enemies with the Berserker's action skill
Killed 15 enemies with the Soldier's action skill
Race around the Ludicrous Speedway in under 31 seconds
Play in a co-op game with either an employee of Gearbox or someone who has this achievement
Rescue enough Claptraps to earn 42 inventory slots
Completed the "House of the Ned" mission
Completed the "Jakobs Fodder" mission
Kill Ned
Actually kill Ned
Complete the "Braaaaaaaaaaaaains!" 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
Built the New Car: Monster
Rescued Athena
Destroyed the Lance Depot
Destroyed a Lancer while in a Racer
Reached Level 61
Paid for a worthless tour of the world's largest bullet
Kill Crawmerax the Invincible
Kill each of the loot midgets
Complete all missions in Secret Armory
Reached Level 51
Knoxx is at rest...finally
The Commandant is dead-trap
Killed Ned...again and again and again
Defeated the Interplanetary Ninja Assassin Claptrap
Completed Tannis' crazy request
Collected 5 3D glasses
Find all 6 Claptrap Statues
Find 25 oil cans
Collect 15 claptrap bobbleheads
Collect 3 panties, 5 fish in a bag, and 15 pizzas