First X Purchases Discount

This extension adds a new condition type to Magento's "Shopping Cart Price Rules". The condition is called "# Times Purchased" and is found in the "Actions" tab.
Since the extension takes advantage of Magento's native rule/promotion system by simply adding a new condition type, you still retain the flexibility you need to offer your customers discounts.
With this, you can construct a discount (no coupon code required) for new products. Simply set the "# Times Purchased" to be less than or equal to (<=) your desired # amount of inventory to discount.