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