My children get no allowance at all.
Here's my view on it, and I'm not saying this is right or wrong, just my opinion....
The purpose of allowance and chores as I see it is to a) instill a sense of value to time and money (and savings) b) help around the house and c) give the kids some money in their pocket to buy stuff for themselves.
Well, my children are expected to help around the house (read, pitch in) and this should not be a paid event. Their rooms must be presentable, clothes cleaned, bathrooms kept cleaned, help out with cleaning common areas, what have you. If someone is not pulling their weight, it's up to the parent(s) to determine the course of action to bring them up to speed. In my eyes, keeping everything presentable is not to be rewarded, it's expected.
Now, in order to heighten my children's sense of the value of money, I remember back to my days when I was younger and saw the time value of money. Not to age myself too badly - but I had a savings account and I had a passbook as a child. I used to go to the bank every month or so and have my interest earned printed in the book and how by putting more money away would only compound more interest and thus more money for me. Today's interest rates are a pittance, so we have decided to start a bank for our kids where we hold their money and pay them 5% interest on their savings account. They are free to deposit and withdraw as they please and every month we produce a statement of account showing their interest. If we are out somewhere and they see something they reallllllly want, they don't have to worry about carrying money around with them, they can make an on the spot purchase and we deduce the money from their account.
In my eyes, if you have your kids carrying around money, they are going to spend it, and spend all of it. The schools around here have a monthly 'spirit cart' fundraiser type deal where they sell the most worthless crap but these kids eat it up. If my youngest brought in 10 dollars with her, she would spend every last penny and come home with plastic pencil sharpeners, erasers, etc.. even though we have all of this stuff in house. So, we do budget that type of spending.
As far as what our children can do for money, they can work

or they can go above and beyond and we have a sheet printed out of extra stuff that can be done on occasion and the value associated with it. This is not a recurring/weekly thing, just when stuff needs to get done. I guess I've always felt that an allowance was counter productive and caused more problems than it was actually worth. I think our kids primary job should be school. Oh, and we do pay/reward for good grades.
I do like the idea of children donating a portion of their money and will try to think of a way to incorporate that into their thinking, although forced donating to me, defeats the purpose and the reason for the donation. Will need to put more thought into that.