on that note: a wink from a sexy, good-lookin' guy passing you on the street a lingering kiss on the hand from a world-famous diplomat/whatever a long, appreciative look from a movie star hunk you've just been introduced to [i've experienced them all more than once and it sure did 'brighten my day'!]
Well it depends on what you're writing, I know for a fact that a lot of 'happy' things depress me actually. Like children laughing, most people would use that in the 'typical' happy scene, I always get sad when I hear kids laughing, same with seeing people with their pets, or seeing the sun sine out my window. All that depresses me. So, to answer your question, I'd have to say seeing an ant colony sprout up, seeing how green the grass is after a thunderstorm,seeing leaves uncurling on the first days of spring, basically the knowledge that life goes on after the worst has happened. But as I said, it depends on what you're writing, your character might hate plants, might love snakes and so seeing a snake hatch out it's egg might make their day brighter, or seeing a lizard sunning itself.
I'm sort of surprised no one has suggested something about a lover of sorts. I haven't really seen anything of that fashion at all. IE: Rolling over and seeing your lovers beautiful/gorgeous face and the gentle stirring of the breath born of peaceful sleep. OR Coming down stairs in a gruesome fog, and hearing the graceful and merciful sound of your beloved's laughter that lifts the troublesome air. As for the few folks that sun causes depression for them, or any happy thing in general, I'm sorry.
The sound and view of water running down a pebbly beach back to the sea after a wave has crashed on shore. The sound and view of wood pigeons making their "we don't like nothin' " calls....their calls have a certain melody and rhythm, and these words fit a treat. The sound (not the view) of people having an argument in which I'm not involved. Drunk clouds bumping into mountain tops. The clap and flash of lightning, the closer the better. Someone snoring at three in the afternoon. My dog's nasal whimper when it wants attention. Somebody else's CD jik-jik-jikking.
^^^^^ It's onomatopoeia. I have a music CD but the audio sticks on the second syllable of the word "magic" not-stop until I do something about it. So I hear "gic gic gic gic gic". Well, "gic" looked a bit odd for what I wanted, so I changed it to "jick". I then thought this looked like a spelling mistake, so I took out the "c". Hey presto! I have a new regular verb - to jik: The action of a faulty audio CD repeating endlessly a very short section of the sound. My CD was jik-jik-jikking.
Waking up in your significant other's embrace. The sound of breakfast being prepared (Bacon/eggs sizzling, Toast popping etc) Hearing the washing machine bleep and having you favourite (Article of clothing here) freshly cleaned. Sound of your pet (Dog parking, cat purring, fish bubbling...) A positive message on your answering machine. Ubeat, uplifting music (perhaps favorite song) being played on your alarm clock. Good news on the radio/newspaper/T.V.