Plenty of folk songs but songs which went really well in the past were:

SO HAPPY TOGETHER - This is an old pop, but is away from the usual mish mash, golly gosh and simply states what a really good marriage is all about.

WIND BENEATH MY WINGS - Goes without saying - brilliant

In the more traditional Irish vein there is: TAKE HER IN YOU ARMS - upbeat and to the point

LAKES OF PONTCHARTRAIN - tissue job though ,