I've been using the new shipping integration in amazon.com's seller interface, and loving it.
You can just click "buy postage" directly from your order view page, and it lets you print out the postage from the next page, automatically marks the item shipped, and even sends an email to your buyer.
I got an email from amazon that shared other sellers' reaction to this new feature:
"Sellers have been raving about the convenience, plus you�ll also receive discounts on USPS Delivery Confirmation and Express Mail.
Using this new service, you can purchase USPS postage directly through your Manage Orders page. To start the process of buying postage for an order, click the Buy Postage button under an order's Product Details section. For more information, please access your seller account and view our Help pages.
One advantage of the Marketplace Shipping Service is that sellers can purchase USPS Delivery Confirmation for First Class and Media Mail for $0.19 per package, and receive free Delivery Confirmation for Priority Mail.
�I actually saw the button for the first time last night and felt like throwing a party. At Christmas time we actually have to close our products on Amazon because the processing time it takes to cut and paste all the info for shipping takes too long (we also have a website). We were so excited to see that Amazon has implemented this service. This is going to be a HUGE asset to us and just the perfect feature to add. We will now be investing more time and products for the Amazon system now that orders can be processed that much faster. GREAT JOB AMAZON!!!!�
"Before I had to print out labels for my return, to the addressee, and then go to USPS.com to figure out postage cost for MEDIA. I could not print out a label or postage there so I had to do my own and use stamps. Now, all in ONE SHOT! I LOVE IT!"