Here's a few of mine:
My personal favorite level: Treasure Hunt: Ancient Pyramid!
A non-linear level. In the first half you have to explore and find the coins to get the key to the pyramid. In the second half you venture into the pyramid itself!
Code: (4421-0000-01F9-E3D8)
My most popular level: Spaceship Shakedown (V.20)
Sneak aboard Bowser's spaceship!
Code: (D0E5-0000-00D7-CF38)
My hardest level: Super Mario RPG: Smithy's Factory
An artistic re-interpretation of Smithy's Factory. Try to survive.
Code: (6A63-0000-014B-9CFD)
EDIT: I took down a level for tweaking.