Allowance Suggestions

About 6 months ago, Monika had ask for an allowance, Katie and Jenny became excited too. At that time, Dave and I were at indifference, I grew up on allowance he didn't. We decided to take 20 dollars out of each of their bank accounts and let them have it in their piggy banks. The girls did well and not spend it all right away.
This Christmas, the girls really got into wanting to buy gifts for people. In the years past, I would buy all the gifts and have them help wrap "their" gifts that they were giving to others, but this year, they picked out for each person, needless to stay it was a more expensive Christmas, but oh the smiles and joy they got out of giving their gifts was priceless.
The girls do a lot of "helping out" around the house. They make their bed everyday, they help with setting/preparing and clean up at mealtimes, they clean living room (one of the main places they play) and assist with laundry. This is something they have done since they were really little. When I am in my "deep cleaning" mood, they will help out with vacuum and dusting everything and do a very good job on that. They like to help shovel the driveway.
Dave and I would like to have them continue doing the helping out things without "paying" them anything. We are looking for suggestions on creative ways for them to make money, so they can buy things and learn that if they want something more expensive and it just a "toy" like item, they need to work on saving up the money for it. They don't always understand why we can buy some things they want and other things I say no we don't have the money or you don't need that....The girls ages are 7,6,6. We feel this is a great way to show them how to manage money and to save for thing, but we don't want it to interfere with all the "helping"they do.
Dave and I are very thankful on how much our girls help out and that they do it without complaining. One girl might not feel like helping, but one or both of the other girls will step in. The one/ones that help out get praised from us, if one doesn't feel like doing it (with the exception of making the bed and cleaning up their mess), we don't say anything to them.