Quality skin, shape, hair, eyes, poses, AO are essential finds on SL.
Amacci (SLurl) is a huge store spread out in several buildings, full of hairs, eyes, skin and shapes, poses & AO, and jewelry. They offer a couple of free gifts for everyone and a newbie gift for those who are younger than 14 days. Great store to look around in, when you want to know what avatars can look like.
You need clothes too of course. On SL anyone can find their own style.
For the fans of haute couture, Mimi's choice (SLurl) offers a great collection of fashion from several designer stores. Scattered among the displays you'll find gifts, freebies, dollarbies and a bargain booth. They also have a store for men with gifts and a bargain booth.