For those interested in such things as the
relative difficulty[/b] of one piece from the piano repertoire compared to another, I find the RCM Syllabus very helpful. In actual number of pieces listed, it is much more comprehensive than anything I have seen from the ABRSM or the Trinity lists. 
In each of Grade X and ARCT lists, pieces are listed in :
List A : Works of J.S.Bach
List B : Classical Sonatas (Beethoven, Haydn, Mozart,)
List C : Romantic Repertoire
List D : 20th-century Repertoire
List E : (Later) 20th-century Repertoire
The ARCT list also has a separate listing of "Concert Etudes"
A new Syllabus has just been published replacing the last one published in 2001; my local music store expects it in this week. The last piano syllabus (2001) was published by Frederick Harris Music www.frederickharrismusic.com
but I don't see the new Piano Syllabus on their website, but I presume they are still publishing for RCM.
 Examples :
List A : 31 works by J.S. Bach
List B : 21 Sonatas by Beethoven, Clementi, Haydn, Mozart
List C : 50 pieces
List D : 49 pieces
List E : 47 pieces
List A : 41 works by J.S Bach
List B : 42 Sonatas by Beethoven, Clementi, Grieg, Haydn, Mozart, Schubert
List C : 86 pieces
List D : 66 pieces
List E : 100 pieces
Concert Etudes : from Weber to Ligeti, including such observations as
Chopin : any one except Op 25 No 2
Debussy : any one
Ligeti, Etudes for Piano, bk 1: any one
Liszt Paganini Etudes: any one except "La Chasse"
etc., etc., which makes a very large number of Etudes from which to choose.