I know I've recommended Etsy Hacks before but now I want to give a rundown of what I think are the best scripts. To run Etsy Hacks you need to use Firefox with the Greasemonkey add-on installed.
fast tagger: Add all your listings' tags at once. Makes tagging much faster, especially for users with slower internet connections.
bulk image uploader: Upload up to five images at once when editing a listing. Maybe not the best option for slower connections but a time saver for broadband users.
renew listing: Renew a listing from the View Listing page.
copy listing: Quickly create a new listing based on an existing one. The single most useful Etsy Hack if you have a lot of similar items that only need minor editing to make the listing unique. This hack doesn't copy images but covers title, description, tags, price, and shipping.
shop tools: Adds a links to shop configuration pages to your shop and listing pages.
edit this item: Adds "edit item" and "delete item" links to the View Listing page when viewing an item in your shop.