Peach's Crown

Princess Peach's Crown is Princess Peach's emblem and a symbol of the Mushroom Kingdom.

Nintendo Comics System
In the Nintendo Comics System issue Cloud Burst, Princess Peach has lost her crown and needs it for her yearly recoronation, so she sends Mario and Luigi to retrieve it. She believes King Koopa to have stolen it as he is invading "World 3". In reality, it was stolen, along with King Koopa's crown, by a Lakitu and the plumbers eventually get it back for her.

Super Mario RPG: Legend of the Seven Stars
In Super Mario RPG: Legend of the Seven Stars, Princess Peach loses her crown during her wedding to Booster and Mario has to find it. Mario eventually finds the crown on top of Booster's head. Depending on how fast Mario finds this and a bunch of Princess Peach's other items, he may receive a kiss from Peach (if he does it very slowly, Booster, Bowser, or even both may kiss him).

Mario & Luigi: Partners in Time
In Mario & Luigi: Partners in Time, Peach's crown can be found on the top of the Thwomp Volcano.

Super Mario Galaxy
In the Wii game Super Mario Galaxy, the Toad Guards feature a picture of Princess Peach's crown on their shields.

Super Mario Galaxy 2
In Super Mario Galaxy 2, Banktoad carries a shield with a picture of the crown after being given at least 2000 Star Bits.

Trivia

 * A treasure in Pikmin 2 looks very much like Princss Peach's Crown.
 * In Super Mario 3D World, Mario, Luigi, and even Toad lose their headgear when in their small forms, but Princess Peach does not lose her crown.