Guide to the pianist's repertoire / Maurice Hinson. 3rd ed.
Bloomington : Indiana University Press, c2000
MUSIC Ref ML128.P3 H5 2000
Concert piano repertoire : a manual of solo literature for artists and performers
Metuchen, NJ : Scarecrow Press, 1974
MUSIC Ref ML128.P3 F39
A guide to piano music by women composers / Pamela Youngdahl Dees
Westport, Conn. : Greenwood Press, 2002-
MUSIC Ref ML102.P5 D44 2002
Piano music in collections : an index / Rita M. Fuszek
Detroit, Mich. : Information Coordinators, 1982
MUSIC Ref ML128.P3 F87 1982
Clavier, v. 1 (1962) - v. 47 (2008) ML1.C79
Clavier companion, v. 1 (2009)- ML1.C792
The piano quarterly, no. 34 (1960) -159 (1992) ML1.P66
Piano & keyboard, no. 160 (1993)-208 (2001) ML1.P66
M - Scores
M20-39--Solo piano music
M198-213--Piano with 3+ Hands
M1010-1011, M1110-1111--Piano with orchestra and string orchestra (includes full scores and solos with piano arrangements)
ML - Music Literature
ML128.P3--Piano music: Bibliography
ML649.8-747--Books about the piano
MT - Instruction and Study
MT220-258--Methods, etudes, etc.
Concertos (Piano with string orchestra)
Piano with orchestra
...and there are lots more. Do a subject search for "piano" and see the 426 different subject headings that begin with "piano."
... and lots more. Search "piano" in Encore and find more than 1000 books, more than 6900 recordings, and more than 18,000 scores.