For example, the Time Machine: you can see Etsy listings almost in real time as they are submitted, as well as go back in time and view older Etsy listings.
The Etsy Sampler is a great way to get a general "feel" of what Etsy has to offer. You have a few options here: you can browse 100 different sellers, you can view top sellers, top items, random items, or recently sold items (to see what got away from you!).
One of the most interesting Etsy features has to be the Shop By Color tool. Wave your mouse around on this page to see what colors are available, and then go ahead and click through. This is a GREAT way to locate just the right artpiece for your living room (just an example).
The Etsy Geolocator allows you to browse sellers that are located near you...or not. This could potentially save you some money on shipping (especially if you're looking for something large).
And if that's not enough Etsy search goodness for you, you can also search by browsing through the many Categories, or Materials and Tags. Believe me, once you start looking around Etsy, it will be hard to tear yourself away - there are just so many wonderfully talented people here and the site is absolutely lovely.