I was required as a foster parent to give a weekly allowance, which I did. They get $5 a week, which is not tied to chores, because that's just something they have to do, period. I love their allowance, because I enjoy taking it away.
The best is for babysitting. If they are bad for the babysitter, the babysitter gets combat pay, and they reimburse me. The other day, my son had to pay for a uniform sweatshirt, as he had lost the one I'd gotten him. And, occasionally, they actually keep their allowance and even save it! They can use it for the farmer's market day at their school, for books, for buying popcorn from the concession stand at school sporting events, etc. And for gifts for the family, of course.
I did learn of a program online to help kids learn responsibility called payjr.com. It also tracks chores, and the kid doesn't get paid until the chore is done, that kind of thing. You might check that out.