"Piano Notes" by Charles Rosen
"Piano" by Louis Kentner. an older book but I think it is still in print in paperback. One of the Menuhin Music Guides.

There are so many books for pianists that are of limited interest, but I found the above two to be worthwhile  exceptions. (Allan)

Recommended reading for string players:

"Chamber Music Repertoire for Amateur Players - A guide to choosing works matching players' abilities" by Harold Haynes. ISBN 0 9524572 2 9

"Lists the whole 'standard' repertoire and hundreds of little known works, with assessments of the difficulty of each part (except wind). Though half of the book is for string quartets, there are also works for some 110 other combinations of instruments." A real labour of love! One of the string quartets listed is "And it was Summertime" by club member Audrey Podmore, so I must confess to some vested interest!  (Audrey)