If you are using USPS shipping services, then this extension is the perfect choice for you. It can create USPS shipping labels. Stamps.com API access to USPS shipping rates to create labels, though these rates won’t be shown to customers at checkout, for that you need to install USPS Shipping Methods extension in your store.
This is the EXACT same plugin as distributed by the developer on WooCommerce. The developers’ links are provided above.