My DDs were 6 and 9 when we went in July 2007. For about 6 months before our trip, they started earning money - - extra chores (we don't give "allowances" for their normal chores, they just have to do them!), lemonade/bake sales, garage sale, car washes, etc.
They ended up with about $150 each, and we put it on Disney gift cards. I wrote each girl's initial on their card with a Sharpie, to avoid confusion.
It totally put an end to any begging for mom and dad to buy them things! They were VERY good consumers, too! They each ended up with a shirt, a hat, pins, mugs, beanie babies, jewelry, and gifts for their friends.