I'm not sure exactly what you mean by "wedding song", but here are the songs Klinkman and I have selected for our wedding:

Processional (walking down the aisle): In My Life by The Beatles

Lighting of the Unity Candle: Grow Old With Me by John Lennon

Recessional (walking back down the aisle with my new husband!): A Life Less Ordinary by Carbon Leaf

First Dance: Chasing Cars by Snow Patrol

Bride/Father of the Bride Dance: My Girl by The Temptations

Not sure if we'll have a Mother of the Groom/Groom dance yet or what the song will be, I'll leave that up to my fiance.

As for your other questions, I really don't think I have a favorite song or favorite slow song per se...for me, music really is all about fitting with or changing my mood, so my feelings about a particular song really depend on my mood/what I need or want to listen to at the time. Of course there are probably standbys that I'll always enjoy, but they are too numerous to mention here.