Liszt - Liebestraum
The structure is a little different, but you get the same melody being elaborated on throughout the piece (with two kick ass cadenzas!). It's probably a little bit easier, and doesn't start as intense. After the first cadenza you get all these awesome key changes. What I love about this piece is that it's so playable! There aren't any awkward passages whatsoever, and with practice anyone with any size hand can play it (as in there aren't the gigantic chords that half of pianists can't reach, or these ridiculous double note figurations that you'd see in other Liszt stuff).
Rachmaninoff - Prelude in G# minor
A little different in structure, many interludes throughout the piece. Probably around the same level as Fantasie Impromptu (it's got larger leaps and a more difficult left hand in my opinion, but the right hand passagework isn't as bad). A very distinct melody throughout, and one awesome thing about this piece are all the other lines you can work around with to complement the melody.
Chopin - Etude Op. 10 #12
Fast left hand, intense melody with right hand. You've probably heard this before

Debussy - L'Isle Joyeuse
Different difficulties than the rest of the pieces; this one has very strange harmonies (compared to the other ones!), whole tone passages, and pretty noticeable meter changes with polyrhythms. I'd probably say that this is the most difficult out of all of them based on what I've seen previously on the forum (but I'd probably have a harder time performing the revolutionary etude because my left hand is not that good), but this has some fast-as-hell passages with arpeggios, strange melodies, and is about 5 minutes long. Check it out!