I like the categorization of prayer into A-C-T-S: that is, adoration, confession, thanksgiving, and supplication. Every night, I run through that list and try to recall events of the day that fit into each box. I’ll admit, though, that the first category is the trickiest, especially since it’s very easy to say you adore God for everything He does for you, which suggests that it’s really not much different from thanksgiving.
But it’s worth maintaining a distinction. When I search for things at evening prayer to adore God about, the most common involve nature, love, and complexity (perhaps this last should be combined also with the “richness” of life). And I think what all three have in common are high degrees of positivity and inexplicability.
And that makes sense. You aren’t going to adore someone for something they’ve done or created that is negative. Note, by the way, that the positivity may not even be something aimed at you; it’s just something you observe in some way. And it has to be very powerful, too, to trigger the feeling we call adoration. Seeing a sand castle doesn’t cause adoration for the builder; seeing the firmament does. That some creatures might fear each other is not surprising; but often the love in our lives is. And the very complexity of our world and, in particular, of human lives and activities in the world is, to me, literally awesome.
Let me add a fourth category of adoration (and I’m not suggesting that what I can come up with is all there can be): music and, for that matter, any powerful art. Again, no denying its positivity, and it’s often very hard to explain why a song or a poem moves us to tears.
Oh, and here’s a fifth: laughter. Once more, highly positive and defying explanation. What a great gift God gave us when He created us to laugh. We should adore Him for it.
Postscript: The inexplicability aspect, especially, also means each of these can lead us to believe in God in the first place.
Second postscript: This site’s post on Timothy Keller’s book Prayer: Experiencing Awe and Intimacy with God quotes the passage on page 197 of that book in which C.S. Lewis discusses adoration.
Third postscript: And shouldn’t Scripture — the Word of God — be on the list? There are elements of both complexity and art in it, but its wonders go beyond that. And it is of course positive and it can be a mysterious. So I would bear it in mind when you thank God for His wonders that you might have experienced that day.