The following are definitely familiar and most popular light music works:

Love is... I

Love is... II

Stepping On The Rainy Street

Rivers Flows In You

My Soul

Piano Music at Night (5)

The Mark of the Rain

I've had a cold in that corner (both the vocal and piano versions are good)

The theme song of "Forrest Gump" (I'm forrest. ..forrest gump)

Kikujiro’s Summer (Summer)

Somewhere In Time (Pure Music)

Tears

The following is me Other recommendations:

Canon

Wedding in a Dream

Whispers of Autumn

Adelina by the Water

Memorial of Love

Moonlight on the Sea of ??Clouds (soundtrack for "Castle in the Sky")

いつも何多でも (pure music version of "Spirited Away" soundtrack)

Go Home

Annie's Wonderland

Snow's Dream

A Girl's Prayer