I realized during the last few weeks that many customers don't know where to shop beyond the familiar online retailers or portals. Of course it depends on what you want to buy. I usually ship clothes, shoes, bags, partyware, toys [for both kids and adults ;-)], bakeware, accessories, gadgets (not limited to smartphones/tablets, I've shipped two huge watchwinders!) and vintage items/collectibles.
You have many options to choose from. While unfamiliar sites may be "risky" but a little bit of online research can help you decide if the site/seller is reliable. I go bargain hunting at retailer's affiliates such as MyHabit, 6pm. For gadgets or unusual stuff, I like ThinkGeek and Fab. The fashionistas will be familiar with Net-A-Porter and Zappos. If you do a bit of research, you will find many of these sites are now owned by big names that wants a piece of the "outlet" market but not wanting to extend their brands.
The early adopters will go hunt for future products (future because it is usually still in concept stage) at Kickstarter or Indiegogo. Those who love handicrafts or vintage items will find Etsy a viable alternative to eBay.
If you don't know where to begin, just ask. ;-)