Here is the full list of all 37 LEGO Harry Potter: Years 1-4 trophies - there are 18 bronze, 14 silver, 4 gold and 1 platinum.
Collect all the bronze, silver and gold trophies
Defeat Harry (as Voldemort), in the Graveyard
Defeat Quirrell in the Quirrell boss fight, using Voldemort
Complete the game to 100%
Buy every version of Voldemort (Quirrell/Tom Riddle/Voldemort)
Collect all of the Gold Bricks
Destroy 50 Devil's Snare plants
Unlock all Animagi
Collect all of the house crests in Year 4
Rescue all students in peril
Get True Wizard in every level
Collect all of the house crests in Year 3
Collect all of the house crests in Year 2
Buy the entire Weasley family
Buy the entire Gryffindor Quidditch team from Book One
Defeat 10 enemies with a Muggle character
Collect all of the house crests in Year 1
Defeat the mountain troll, using Quirrell
Collect 10 million studs in one level
Collect all of the Red Bricks
Hide in a barrel as Snape
Scare 20 students using a ghost character
Complete Year Four Story Levels
Complete the Story Levels in all four years
Complete All Story Lessons
Use the Time-Turner
Complete Year Three Story Levels
Complete Year Two Story Levels
Defeat 20 spiders with Ron
Complete all the LEGO Builder tutorial levels.
Knock over ten characters using a ride-able object
Complete Year One Story Levels
Defeat 20 enemies with Fang
Freeze 20 characters using Glacius
Turn the sound down to 0 and music off in the options menu whilst in the library
Complete the Quidditch level within five minutes
Collect 500 ghost studs