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 the Vault Boss
Discovered Eridian Promontory
Discovered Crimson Lance Enclave
Earned level 30
Killed Flynt
Killed the Rakk Hive
Discovered Trash Coast
Killed Krom
Discovered Krom's Canyon
Completed 5 missions in the Rust Commons
Discovered The Scrapyard
Reached proficiency level 10 with any weapon type
Sold 50 guns to a shop
Killed an enemy plumber-style
Equipped a class mod for your character
Earned level 20
Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Killed Sledge
Earned $1,000,000
Won a duel against another player
Won a duel without taking damage
Gamed with fame
Applied an elemental artifact
Discovered Headstone Mine
Discovered Sledge's Safe House
Killed 25 enemies with incendiary weapons
Killed 5 Rakk in under 10 seconds
Killed 25 enemies by ramming them with any vehicle
Earned level 10
Killed 25 enemies with explosive weapons
Killed 15 enemies with the Soldier's action skill
Earned level 5
Discovered Skag Gully
Completed 5 missions in the Arid Badlands
Complete all missions in the Arid Badlands
Complete all missions in the Rust Commons
Master the technology of Pandora
Race around the Ludicrous Speedway in under 31 seconds
Earn level 40
Earn level 50
Win an arena match
Rescue a groupmate from death in a co-op game
Complete 15 missions in co-op
Kill 25 enemies with corrosive weapons
Kill 25 enemies with shock weapons
Rescue enough Claptraps to earn 42 inventory slots
Kill an enemy with the Siren's action skill
Kill 15 enemies with the Hunter's action skill
Kill 15 enemies with the Berserker's action skill
Completed the "House of the Ned" mission
Complete 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
Build the New Car: Monster
Rescue Athena
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
Reach 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