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