The Pearl Fishers Duet - has me in floods every time. There are so many versions, most of which are great, but I looove Bryn Terfel so this is a good one. Bit crackly but still worth a listen.
I also love Streets of London - in fact, I am singing it at a concert in a few weeks!
Back in the 80's a friends husband was killed in a road accident and she had The Power of Love played at the funeral. I still find it hard to listen to when it crops up.