Ideas, Anyone?

We - someone and I - need a song to sing for someone's wedding. It isn't easy looking for a suitable one as:

1. It must be a song about love, being in love:
I'd really prefer it if we don't sing about "you" specifically, because that's sort of like serenading just one in the couple, which, if you really think about it, is very odd. For example, we considered "Close To You" by Carpenters - it's a who-wouldn't-like-it song, obviously, but it's lyrics are basically praising just the guy. Well, also, we test-sang it in karaoke, and it sounded boring. (Fine... we're not as talented as Karen was)

2. If it is a duet, both voices must be of about the same range:
Since two female voices will be singing, it'll be awfully weird if one had to sing the manly man's part. My duet partner has an amazing range, and can go pretty low when she wants to; I suppose I could sing low too, but it still remains that both of us will make a very odd-sounding baritone.

3. If it is a solo, it must have a nice version sung as a duet:
We are not pros. We are not formally-trained in song arrangements - we do not know how to come up with harmonies unless we have a reference. Simply taking turns singing several lines at a time, and then the chorus together is so cacat. No, we'll not settle for a solo for two unless we can sing at least the chorus as a two-part harmony.

4. It must be one simply-accompanied:
We want a song with minimal music accompaniment - something simple and beautiful. It is not that we do not want the music to outshine our vocals (it probably will, any ways...) It's just that we'll have only a 3-piece band backing us up. We can't do any songs that would sound good only when sung with a 5-piece rock band, or a 60-piece orchestra, or a 30-strong choir doing backup vocals. A quietly-moving, lyrically-meaningful and sentimental piece would be perfect!

5. It is best if it isn't an over-sung piece:
Well, such as Shania Twain's "From This Moment On", Bryan Adams and Barbra Streisand's "I Finally Found Someone" (not that I don't absolutely love it to bits), Ronan Keating's "When You Say Nothing At All". We want a song that is ideal for a wedding, not a song that is expected to be played at a wedding. Of course, the reader would have also noticed that the examples mentioned don't fulfill points (2) and (3) as well.

And I wonder why we find it so hard to decide on what to sing...
*arghhh*