iTunes 10 for Mac: View your purchase history
You can see a list of all your iTunes Store purchases.
To view your purchase history:
Choose Store > View My Account.
In the Account Information window, click Purchase History.
The purchase history shows purchases made using this account, with your most recent purchases shown first. To view details of previous purchases, click the arrow to the left of the order date. If your purchase history seems incomplete, make sure you’ve clicked the arrow next to each previous purchase to see all your purchase history information.
If your purchase history seems to be incorrect, or you believe you’ve been charged for an item you didn’t buy, visit the iTunes Store Support website.