As the worship leader of my church, I always try to make sure the songs I choose are singable by everyone in the congregation, not too high and not too low. I also like to mix older worship choruses with some newer material, as well as hymns, so there's something for everyone.
I've recently been attracted to Keith Getty's material. He writes modern hymns--easy to sing, beautiful melodies, and they can easily be arranged for solo piano or with a full band.