This is an older thread, but I think that demanding "evidence" for the existence of a higher power defeats the VERY purpose and foundation of faith and spirituality itself. I suppose some people could point to Near-Death Experiences for example, as possible "evidence" for some kind of afterlife, although skeptics will dismiss those also.
I think it is in the end,
something deeper, from the "heart", from your personal intuition, if you will, that true belief and prayer is founded upon. Religion is not something you can necessarily "prove" or "disprove" like experiments in a certain laboratory, it is something very profound and personal.