I think (ahhh, dangerous words those - means an opinion's coming!) DaveO nailed it on the head when he talked about "spiritual experiences". I'll just put in my usual "I'm not religious" disclaimer here, but if religion is a feeling or an emotion at the amazing beauty and wonders of nature, then with the risk of sounding trite, I'd say that the best "religious" experiences are those moments when we "feel" a sense of awe and a welling up of emotion. It's like the "homesick" feeling where you're homesick for something - some time, place or emotion, but you're not sure what it is, just that you want to experience it.

For A-Level English I had to read D.H. Lawrence's "Sons and Lovers" and I couldn't stand it - I found it depressing and disturbing, but reading papers about him I remember coming across a quotation about his view on religion being the moments when you are toatlly aware and in awe of nature. I tried to find that quotation to add here, but couldn't locate it, but I did find this one, which is perhaps even more relevant:

"Brute force crushes many plants. Yet the plants rise again. The pyramids will not last a moment,compared with the daisy. And before Buddha or Jesus spoke the nightingale sang, and long after the words of Jesus and Buddha are gone into oblivion, the nightingale still will sing. Because it is neither preaching nor teaching nor commanding nor urging. It is just singing. And in the beginning was not a Word, but a chirrup."
-- Sketches of Etruscan Places, Tarquinia