Jewelry intended specifically to be worn in
piercings beyond the standard
lobe. This requires different specifications than normal
jewelry. Body jewelry should be made from high-quality (read: small amounts of
nickel that's securely trapped - this prevents irration and metal allergies) stainless steel, high-quality
gold (same disclaimer applies),
titanium,
niobium (controversial - some people say yes, some say no), medical-grade
plastics,
PTFE/
Teflon,
pyrex glass, or various certain organic materials such as
bone or some
woods. All of these materials should be okay for short periods of wear, but the best for long-term use are titanium and stainless steel. The only materials appropiate for freshly pierced or stretched holes are stainless steel, titanium, PTFE/teflon, and maybe niobium. Body jewelry should be highly polished and free from scratches or ridges. Barbells should be internally threaded, where the beads on the ends have the protruding threads.
There are innumerable types of body jewelry. The most common are barbell, curved barbell, captive bead ring, nostril screw and labret. One of my personal favorites is the eyelet. There are also lots of things to do with the materials themselves. Titanium and niobium can be oxidized to produce color. Acrylic plastic jewelry can be UV fluorescent: nothing's better under black light. Avoid glow-in-the-dark jewelry - there's some questions about carcinogens, so why bother.
Some good places to buy body jewelry on-line are Anatometal and Custom Steel. Watch out - there's a lot of crap out there, and bad body jewelry can hurt your piercing in a number of ways.