This is a list of piano/vocal compilations of songs by Sondheim. 
Scores and selections from individual shows are included on that show's main page. 
Chronologically listed.  [Alphabetical Index below.]

The Hansen Treasury of Stephen Sondheim Songs

The Stephen Sondheim Songbook

Lee Evans Arranges Stephen Sondheim

• Anyone Can Whistle [from Anyone Can Whistle]
• Beautiful Girls [from Follies]
• Being Alive [from Company]
• Broadway Baby [from Follies]
• Come Play Wiz Me [from Anyone Can Whistle]
• Company [from Company]
• Good Thing Going [from Merrily We Roll Along]
• I Remember [from Evening Primrose]
• Impossible [from A Funny Thing Happened on the Way to the Forum]
• Johanna [from Sweeney Todd]
• Losing My Mind [from Follies]
• Lovely [from A Funny Thing Happened on the Way to the Forum]
• Not a Days Goes By [from Merrily We Roll Along]
• Not While I'm Around [from Sweeney Todd]
• Old Friends [from Merrily We Roll Along]
• Our Time [from Merrily We Roll Along]
• A Parade in Town [from Anyone Can Whistle]
• Send in the Clowns [from A Little Night Music]
• Sunday [from Sunday in the Park With George]
• Take Me to the World [from Evening Primrose]
• There Won't Be Trumpets [from Anyone Can Whistle]
• Waiting for the Girls Upstairs [from Follies]

All Sondheim: Volume I

• Another Hundred People [from Company]
• Anyone Can Whistle [from Anyone Can Whistle]
• The Ballad of Sweeney Todd [from Sweeney Todd]
• Being Alive [from Company]
• Broadway Baby [from Follies]
• By the Sea [from Sweeney Todd]
• Comedy Tonight [from A Funny Thing Happened on the Way to the Forum]
• Could I Leave You? [from Follies]
• Every Day a Little Death [from A Little Night Music]
• Green Finch and Linnet Bird [from Sweeney Todd]
• I Never Do Anything Twice [from The Seven Per Cent Solution]
• I Remember [from Evening Primrose]
• I'm Still Here [from Follies]
• Johanna [from Sweeney Todd]
• The Ladies Who Lunch [from Company]
• The Little Things You Do Together [from Company]
• Losing My Mind [from Follies]
• The Miller's Son [from A Little Night Music]
• Not While I'm Around [from Sweeney Todd]
• A Parade in Town [from Anyone Can Whistle]
• Poor Thing [from Sweeney Todd]
• Pretty Lady [from Pacific Overtures]
• Pretty Women [from Sweeney Todd]
• Remember? [from A Little Night Music]
• Send in the Clowns [from A Little Night Music]
• Sorry - Grateful [from Company]
• You Must Meet My Wife [from A Little Night Music]

All Sondheim: Volume II

• All Things Bright and Beautiful [cut from Follies]
• Fear No More [from The Frogs]
• Finishing the Hat [from Sunday in the Park With George]
• The Girls of Summer [from The Girls of Summer]
• The Glamorous Life [from A Little Night Music]
• Good Thing Going [from Merrily We Roll Along]
• I Do Like You [cut from A Funny Thing Happened on the Way to the Forum]
• Invocation and Instructions [from The Frogs]
• Isn't It? [from Saturday Night]
• Little White House / Who Could Be Blue? [cut from Follies]
• Marry Me a Little [cut from Company]
• Not a Days Goes By [from Merrily We Roll Along]
• Old Friends [from Merrily We Roll Along]
• Silly People [cut from A Little Night Music]
• So Many People [from Saturday Night]
• Sunday [from Sunday in the Park With George]
• Take Me to the World [from Evening Primrose]
• Uptown, Downtown [cut from Follies]
• What More Do I Need? [from Saturday Night]

All Sondheim: Volume III

• Ah, But Underneath [from the London production of Follies]
• Bang [cut from A Little Night Music]
• Beautiful [from Sunday in the Park With George]
• Country House [from the London production of Follies]
• Everybody Says Don't [from Anyone Can Whistle]
• Goodbye for Now [from Reds]
• Happily Ever After [cut from Company]
• The Hills of Tomorrow [from Merrily We Roll Along]
• Honey [cut from Merrily We Roll Along]
• Liaisons [from A Little Night Music]
• Like It Was [from Merrily We Roll Along]
• Loveland [from the London production of Follies]
• Make the Most of Your Music [from the London production of Follies]
• Merrily We Roll Along [from Merrily We Roll Along]
• Putting It Together [from Sunday in the Park With George]
• Truly Content [from Passionella]
• Two Fairy Tales [cut from A Little Night Music]
• Wait [from Sweeney Todd]

All Sondheim: Volume IV

• Beautiful Girls [from Follies]
• Dawn [unused; written for Singing Out Loud]
• Do I Hear a Waltz? [unused]
• Giants in the Sky [from Into the Woods]
• Growing Up [from Merrily We Roll Along]
• Happiness [from Passion]
• I Remember That [from Saturday Night]
• If You Can Find Me, I'm Here [from Evening Primrose]
• Move On [from Sunday in the Park With George]
• Multitudes of Amy [cut from Company]
• No, Mary Ann [written for The Thing of It Is, unproduced]
• Pleasant Little Kingdom / Too Many Mornings [from Follies]
• Sand [written for Singing Out Loud, unproduced]
• Saturday Night [from Saturday Night]
• Sooner or Later [from Dick Tracy]
• The Story of Lucy and Jessie [from Follies]
• That Old Piano Roll [cut from Follies]
• Theme from Stavisky
• There is No Other Way [from Pacific Overtures]
• They Ask Me Why I Believe in You [written for I Believe in You, unproduced]
• The Two of You [written for Kukla, Fran and Ollie, unused]
• Unworthy of Your Love [from Assassins]
• Water Under the Bridge [written for Singing Out Loud, unproduced]
• What Can You Lose [from Dick Tracy]
• With So Little to Be Sure Of [from Anyone Can Whistle]
• The World's Full of Girls [cut from Follies]

Stephen Sondheim: A Celebration at Carnegie Hall

• Anyone Can Whistle [from Anyone Can Whistle]
• Back in Business [from Dick Tracy]
• The Ballad of Booth [from Assassins]
• The Ballad of Sweeney Todd [from Sweeney Todd]
• Barcelona [from Company]
• Being Alive [from Company]
• Broadway Baby [from Follies]
• Children Will Listen [from Into the Woods]
• Comedy Tonight [from A Funny Thing Happened on the Way to the Forum]
• Getting Married Today [from Company]
• Good Thing Going [from Merrily We Roll Along]
• Green Finch and Linnet Bird [from Sweeney Todd]
• I Never Do Anything Twice [from The Seven Per Cent Solution]
• Live Alone and Like It [from Dick Tracy]
• Losing My Mind [from Follies]
• Love I Hear [from A Funny Thing Happened on the Way to the Forum]
• Loveland [from Follies]
• Not a Days Goes By [from Merrily We Roll Along]
• Old Friends [from Merrily We Roll Along]
• Our Time [from Merrily We Roll Along]
• Pretty Lady [from Pacific Overtures]
• Send in the Clowns [from A Little Night Music]
• Someone is Waiting [from Company]
• Sooner or Later [from Dick Tracy]
• Sunday [from Sunday in the Park With George]
• Waiting for the Girls Upstairs [from Follies]
• Water Under the Bridge [written for Singing Out Loud, unproduced]
• A Weekend in the Country [from A Little Night Music]
• With So Little to Be Sure Of [from Anyone Can Whistle]
• You Could Drive a Person Crazy [from Company]

Stephen Sondheim: Film and Television Songs

• Dick Tracy
• Back in Business
• Live Alone and Like It
• More
• Sooner or Later
• What Can You Lose
• Evening Primrose
• I Remember
• If You Can Find Me, I'm Here
• Take Me to the World
• When?
• The Glamorous Life [from the film of A Little Night Music]
• Goodbye for Now [from Reds]
• I Never Do Anything Twice [from The Seven Per Cent Solution]
• Little Dream [from The Birdcage]
• Theme from Stavisky
• Water Under the Bridge [written for Singing Out Loud, unproduced]