This is a collection of Greasemonkey scripts for Firefox that tweak how Etsy looks and works in some useful ways. You will need to download and install Greasemonkey before you can use Etsy Hacks. Among a long list of features include a printable receipt enhancer, copy listing, item zoom, bulk image uploader, renew listing from item page, and more.
This tool pulls the information from your shop and formats it for uploading to Google Base. Etsy recently retooled their RSS feeds to make them Google Base friendly, but Let's Ets is much easier to use.
Etsy Fee Calculator
Of course you could do the math out for yourself to figure out what $0.20 + 3.5% of an item's price works out to, but this is much faster. This one can even calculate with Paypal fees as well, making it an easy way to work out exactly how much of each sale you get to keep.
Before Etsy implemented Google Analytics support, this was the best way to check your Etsy stats. Even now it's still useful as a quick check for real-time views on newly listed items and to see who has marked your shop or items as favorites.