What are some calm almost sad sounding piano or violin songs?

only instrumentals

Good Enough by Evanescence can easily stand as an instrumental only on piano.
Schindler's List on violin
Ashokan Farewell on violin
The Cradle by George Winston on piano
Love Song to a Ballerina by George Winston
The Cider House Rules on piano

There's alot...but here are some of my fav's...
Mazzy Star "Five String Serenade" album So Tonight That I Might See
Coldplay "The Scientist" album Rush of Blood to the Head
classical song called "Cannon in d"

Claire de Lune by Claude Debussy

pavane for a dead princess by ravel
moonlight sonata by beethoven
some of bach's minor preludes

Try Siebelius Violin concerto! I'll paste in two links. The first is the second half of the first movement. The second link is the second (and the slowest) movement.

Enjoy!

-Stebone

PS the third movement is upbeat, but so awesome, I am going to paste it in now, too.

The Lark Ascending by Vaughan-Williams
Adagio by Albinoni

Violin : Meditation from Thais by Massenet
http://www.youtube.com/watch?v=ObxzdawhM...

Violin : Romance from the Gadfly by Shostakovich.

Piano : Fantasie Impromptu in C# minor by Chopin
http://www.youtube.com/watch?v=ObxzdawhM...

Here is one arranged for either violin and piano : Nocturne number 20 in C# minor by Chopin
http://www.youtube.com/watch?v=ZR2KkA1Jl...
http://www.youtube.com/watch?v=6I4zoyEwT...

I love that last one ; especially on the violin.

There is no such thing as an instrumental song. Songs have lyrics. So there are no violin songs or piano songs.