Here's the full list, 50 in all for the maximum 1,000 gamerscore. The link at the bottom has the achievement icons.
Missing in Action (5)
Save your crew from an overwhelming attack
Very Elusive (10)
Return to active duty
The Convict (10)
Successfully recruit the biotic Convict
The Krogan (10)
Successfully recruit the krogan
The Archangel (10)
Successfully recruit Archangel
The Professor (10)
Successfully recruit the Professor
The Quarian (10)
Successfully recruit the quarian
The Justicar (10)
Successfully recruit the Justicar
The Assassin (10)
Successfully recruit the Assassin
Friend or Foe (10)
Obtain geth technology
Colony Defense (25)
Defend a human colony from attack
The Prodigal (10)
Gain the loyalty of the Cerberus Officer
Ghost of the Father (10)
Gain the loyalty of the Cerberus Operative
Catharsis (10)
Gain the loyalty of the biotic Convict
Battlemaster (10)
Gain the loyalty of the krogan
Fade Away (10)
Gain the loyalty of Archangel
The Cure (10)
Gain the loyalty of the Professor
Treason (10)
Gain the loyalty of the quarian
Doppelganger (10)
Help the Justicar resolve her mission
Cat's in the Cradle (10)
Gain the loyalty of the Assassin
A House Divided (10)
Hack a geth collective
Ghost Ship (25)
Complete the investigation of a derelict alien vessel
Suicide Mission (50)
Use the Omega 4 Relay
Mission Accomplished (125)
Save humanity throughout the galaxy from certain annihilation
Against All Odds (15)
Survive suicide mission
Insanity (75)
Complete the game on the "Insanity" difficulty level without changing the setting
No One Left Behind (75)
Keep your team alive through the suicide mission
Long Service Medal (75)
Complete Mass Effect 2 twice, or complete it once with a character imported from Mass Effect 1
Paramour (50)
Successfully pursue a relationship with a teammate
Head Hunter (10)
Perform 30 headshot kills with any weapon on humanoid targets
Brawler (10)
Shoot and kill 20 enemies while they're knocked back by a punch
Big Game Hunter (10)
Thresher Maw defeated
Tactician (10)
Hit 20 different targets with multiple biotic powers to combine the effects
Master at Arms (15)
Kill enemies with 5 different heavy weapons during the game
Merciless (10)
Make 20 enemies scream as they fall or are set on fire
Overload Specialist (15)
Disrupt the shields of 25 enemies
Warp Specialist (15)
Warp the barriers of 25 enemies
Incineration Specialist (15)
Incinerate the armor of 25 enemies
Operative (15)
Complete a mission discovered by scanning an unexplored world
Agent (50)
Complete 5 missions discovered by scanning unexplored worlds
Prospector (5)
Retrieve mineral resources by scanning and probing a planet in the galaxy map
Explorer (10)
Visit 100 percent of the planets in an unexplored cluster
Power Gamer (10)
Reach Level 30 with one character
Scholar (15)
Unlock 15 new Mass Effect 2 codex entries
Technician (15)
Obtain (10) technology upgrades
Weapon Specialist (15)
Fully upgrade a weapon
Scientist (10)
Complete any research project in the Normandy's laboratory
Fashionista (5)
Personalize your armor in your quarters on the Normandy
Power Full (15)
Evolve any power
Highly Trained (15)
View all advanced combat training videos at Shepard's private terminal.
