One thing that I'm terribly remiss about doing when it comes to photographing people that I don't know is getting their names and addresses so that I can send them prints later. It's not that I photograph strangers a lot, but occasionally I stumble onto a shot and it turns out nice and then I realize I can't share it with the subjects.
The photo here is a great example. I saw these kids (all members of the same family, I think) posing for a photograph on the statue of Alice in Central Park. It looked like a great photo opportunity for me, too, so I popped off a few frames. But before I could search in my bag and find a pen and a business card, the family had disappeared. I'm sure they got their own shot, of course, but I think this angle from the side makes a nice shot and I know the parents would have liked it.
So next time you're out in a park shooting and you happen to grab a good-looking shot of strangers, just politely (and quickly!) offer to send them a copy of the print. It's a nice gesture and you might even make a few bucks selling them extra prints. And by the way, if you know this family--tell them there's a free print waiting for them!