I'm not asking about UFOs in the "alien spacecraft" sense, just unusual, apparently physical objects up in the air. Looking back, I've seen three:
1) glancing out a window when I was a kid, I saw a blue-ish, lightbulb-shaped object fly, very fast, through the night sky from 12.00-6.00. I have no idea what that thing was.
2) looking up into the sky on a beautifully clear day, I once spotted what I assume was a satellite - just a tiny, round white dot, moving very slowly. Obviously it's impossible to accurately judge distances and proportions in these cases, but it looked to be a hell of a long way up.
3) most spectacularly, I once watched a (roughly, apparently) refrigerator-sized, rectangular sheet of something silvery and reflective tumbling end-over-end through the sky over downtown Wellington, New Zealand. I remember that this was at a time when a satellite was expected to be breaking up over that part of the world, so I assume that what I saw was some part of that.