The Toad Express is a pink plane owned by Peach, Mario, Toadsworth, and some Toads. They used this plane to fly to Isle Delfino in Super Mario Sunshine. The plane landed abruptly at Delfino Airstrip as a crater filled with strange Graffiti covered most of the runway and came to a screeching stop, causing Mario, Peach, and Toadsworth to jumble around inside.
In Mario & Luigi: Superstar Saga, Peach again uses this plane to get to the Beanbean Kingdom; however, when she arrives at the Beanbean International Airport, it is congested by Piranha Plants and the Mom Piranha, preventing the plane from landing. Mario and Luigi got rid of the Piranhas so the Toad Express could safely land. After the player beats the game, the plane is used by Mario, Luigi, Peach, Toadsworth and Bowser to go back to the Mushroom Kingdom (although Bowser was dropped to his castle mid-flight).
In Mario Golf: Advance Tour it makes a small cameo appearance, when it is shown bringing Neil and Ella to the Mushroom Kingdom. It also makes an appearance in Mario Tennis: Power Tour, to bring Clay and Ace.
The plane's interior
Inside of the plane there appear to be four (possibly five, depending on the arrangement) Mushroom-themed seats. There are moderately large windows with elaborate curtains, many fancy details, and a stunning ceiling that is painted (or is possibly a lamp) bright blue with yellow stars and white clouds.