Just to clear up some of the info here:
-- A big difference between Stamps.com and Endicia is that Stamps.com has the integrations built inside our software. So there is no need to download a secondary program as Endicia requires (ShipWorks is required for eBay orders and iABOL is required for Amazon orders). Other marketplaces/payment processors such as PayPal, Google Checkout, Yahoo Stores, and/or shopping carts require a third party program, usually with a fee, in order for the data to be imported into Endicia.
Stamps.com includes the batch import capability in the software for our standard monthly plan at $15.99. Once the connections are established, you can click one "refresh" button and the software will connect to each marketplace/store and import your data.
-- Stamps.com also has a free program specifically for eBay sellers. There is no subscription charge, but the account is limited to only importing orders from eBay. You can see it at http://www.stamps.com/ebayfree1/
With that said, Endicia does have some nice features that Stamps.com does not have yet like Business Reply Mail, Delivery Statistics and other features. Both programs work well and offer big money/time savings compared to going to the Post Office. I'm partial to Stamps.com for obvious reasons ;-)