like the "Fires at Midnight" suggestion; other Tull songs in this category that are not too hard-rockin' might include "The Whistler" and "Acres Wild" but then it may be getting into sex territory there somewhat...
as for traditional songs and folk:
Westlin' Winds
Red is the Rose
Call and Answer (De Danaan did this; I have sung it at two weddings)
I Love my Love
Kellswater
Star of the County Down (ballad version)
The Trees They Do Grow High
Queen Among the Heather (June Tabor does this nicely)
(If I Were a) Blackbird
Searching for Lambs
Ca' the Yowes

torch songs:
Since I Fell for You
Can't Help Lovin' Dat Man
Stormy Weather

peg