There are a ton of pieces I'd love to learn, but that are just too difficult for me at the moment, ones that I think I would just get frustrated trying to learn, and learn to hate. However, I've got a list going of pieces that are within my capabilities that I just haven't gotten around to learning...
In no particular order:
Scriabin - Sonata No. 2
Scriabin - Vers la flamme
Prokofiev - all of Sonata 7 (currently working on just the third movement)
Dvorak - At an Old Castle
Liszt - Consolation No. 3
Liszt - Die Zelle in Nonnenwerth
Brahms - Scherzo, Op. 4
Mompou - Impresiones intimas
Ornstein - Waltz No. 7
Rachmaninoff - Vocalise, Richardson version
Sibelius - Romance, Op. 24/9
Mendelssohn - Liede ohne Worte Op. 30/1
The Door from Sailing to the World
Musique pour la Tristesse de Xion from the Kingdom Hearts piano collection 49410enrique showed in the musical purchases thread
Grieg - quite a few lyric pieces
Rachmaninoff - Nocturne No. 1 in F-sharp minor
Rachmaninoff - Preludes Op. 23/2, 23/4, 23/7, 23/10, 32/5, 32/10, 32/12, 32/13
And for ones that are either too long or difficult for me to devote the time to in the near future...
Rachmaninoff - several etudes-tableaux...actually, basically all of them
Ornstein - Sonata no. 4
Mussorgsky - Pictures at an Exhibition
Hindemith - Sonata no. 2
Chopin - Sonata no. 2
Prokofiev etude op. 2/1
Vine - Sonata No. 1
Rachmaninoff - Concertos 1 (first movement), and then all of 2 and 3
Prokofiev - Concerto 2
Prokofiev - Sonatas 6 & 8
Liszt - Sonata
Schumann - Kreisleriana
Brahms - Concerto 2
Brahms - Sonata no. 3
There's a lot more, but nothing comes to mind at the moment. It's a shame I only have the rest of my life to learn all this!