Every year I head to Kmart for Christmas tree balls and ornaments. The selection isn't as good as when Martha Stewart created a line for Kmart, but you can still find some cute things.
My sister-in-law did really cute trees for her kids rooms last year with trees and ornaments found at Kmart. I copied the theme of my niece's tree for my daughter's room. My daughter couldn't have been more excited about picking out ornaments and having her own tree to decorate and admire, endlessly. Kmart had such cute cupcake and candy ornaments with garland to match. It turned out so cute.