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.
Rescued enough Claptraps to earn 42 inventory slots
Earned level 50
Earned level 40
Killed the Vault Boss
Completed all missions in the Rust Commons
Discovered Eridian Promontory
Discovered Crimson Lance Enclave
Killed Flynt
Reached proficiency level 10 with any weapon type
Killed the Rakk Hive
Discovered Trash Coast
Earned $1,000,000
I bet you never thought you'd be here.
Earned level 30
Killed Krom
Discovered Krom's Canyon
Killed 25 enemies with shock weapons
Discovered The Scrapyard
Completed 5 missions in the Rust Commons
Killed 25 enemies with corrosive weapons
Raced around the Ludicrous Speedway in record time
Mastered the technology of Pandora
Completed all missions in the Arid Badlands
Killed an enemy plumber-style
Earned level 20
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
Discovered Headstone Mine
Applied an elemental artifact
Sold 50 guns to a shop
Killed 25 enemies by ramming them with any vehicle
Rescued a groupmate from death in a co-op game
Discovered Sledge's Safe House
Killed 25 enemies with explosive weapons
Completed 15 missions in co-op
Won a duel without taking damage
Won a duel against another player
Gamed with fame
Killed 5 Rakk in under 10 seconds
Killed 15 enemies with the Hunter's action skill
Earned level 10
Killed 25 enemies with incendiary weapons
Discovered Skag Gully
Earned level 5
Completed 5 missions in the Arid Badlands
Win an arena match
Kill an enemy with the Siren's action skill
Kill 15 enemies with the Berserker's action skill
Kill 15 enemies with the Soldier's action skill
Killed Ned. Again.
Killed Ned...sort of
Completed the "Jakobs Fodder" mission
Completed the "House of the Ned" mission
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
Rescued Athena
Built the New Car: Monster
Destroy the Lance Depot
Kill Crawmerax the Invincible
Kill each of the loot midgets
Destroy a Lancer while in a Racer
Reach Level 61
Complete all missions in Secret Armory
Pay for a worthless tour of the world's largest bullet
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