Achievements for the 360 MAY have been released, these are speculative.
SPOILERS!!!!
Off the Boat 5G
Complete the first mission.
One Hundred and Eighty 10G
In a darts game score 180 with 3 darts.
Pool Shark 10G
Beat a friend at pool.
King of QUB3D 15G
Beat the High Score in QUB3D
Finish Him 15G
Complete 10 melee counters in 4 minutes
Genetically Superior 25G
Come first in 20 singleplayer street races.
Wheelie Rider 30G
Do a wheelie lasting at least 500 feet on a motorbike.
Gobble Gobble 10G
Score 3 strikes in a row, a turkey, in 10-pin bowling.
Driving Mr. Bellic 10G
Unlock the special ability of taxi.
Rolled Over 30G
Do 5 car rolls in a row from one crash.
Walk Free 50G
Lose a 4 star wanted rating by outrunning the cops.
Courier Service 10G
Complete all 10 package delivery jobs.
Retail Therapy 10G
Unlock the special ability of buying guns from a friend.
Chain Reaction 20G
You must blow up 10 vehicles in 10 seconds.
One Man Army 40G
Survive 5 minutes on 6 star wanted level.
Lowest Point 5G
Complete mission "Roman's Sorrow".
Over Fulfilled 10G
Complete all 10 Exotic Export orders.
Manhunt 15G
Complete the most wanted side missions from the police computer.
Cleaned the Mean Streets 20G
Capture 20 criminals through the police computer.
Fed The Fish 5G
Complete the mission "Uncle Vlad".
It'll Cost Ya 5G
Complete a taxi ride without skipping from one island to another.
Sightseer 5G
Fly on all helicopter tours of Liberty City.
Warm Coffee 5G
Successfully date a girl to be invited into her house.
That's How We Roll! 10G
Unlock the special ability of helicopter.
Half Million 55G
Reach a balance of $500,000.
Impossible Trinity 10G
Complete mission "Museum Piece".
Full Exploration 20G
Unlock all the islands.
You Got The Message 20G
Deliver all 30 cars ordered through text message.
Dare Devil 30G
Complete 100% of the unique stunt jumps.
Assassin's Greed 20G
Complete all 9 assassin missions.
Endangered Species 50G
Collect every hidden package in the game.
Under the Radar 40G
Fly underneath the main bridges in the game that cross water with a helicopter.
Dial B For Bomb 10G
Unlock the special ability of phoning for a bomb to be placed.
Gracefully Taken 10G
Complete mission "I'll Take Her".
Liberty City (5) 20G
After meeting all possible friends, the ones left alive all like you above 90%.
No More Strangers 5G
Meet all random characters.
That Special Someone 10G
Complete mission "That Special Someone".
You Won! 60G
Complete the final mission.
Liberty City Minute 30G
Complete the story missions in less than 30 hours.
Key To The City 100G
Achieve 100% in "Game progress" statistic.
Teamplayer 10G
Kill 5 players who are not in your team, in any ranked multiplayer team game.
Cut Your Teeth 5G
Earn a personal rank promotion in multiplayer
Join The Midnight Club 10G
Win a ranked multiplayer race without damaging your vehicle too much and with damaged enabled.
Fly The Co-op 15G
Beat our time in ranked versions of "Deal Breaker", "Hangman's NOOSE" and "Bomb da Base II".
Take It For The Team 10G
Be on the winning team in all ranked multiplayer team games.
Top Of The Food Chain 10G
Kill 20 players with a pistol in a ranked multiplayer deathmatch.
Top The Midnight Club 20G
Come first in 20 different ranked standard multiplayer races.
Wanted 20G
Achieve the highest personal rank in multiplayer.
Auf Wiedersehen Petrovic 30G
Win all ranked multiplayer variations, all races and "Cops 'n Crooks", as both sides.
http://www.xbox360achievements.org/news/news.php?id=885