Titanium band rings, several set with cubic zirconia.
Why titanium for a band. It weighs about half what steel does, will not corrode, and is hypoallergenic — the choice if other metals irritate your skin, or if you have never worn a ring and want one you will not notice.
Sizing caution. Titanium cannot be resized by a jeweller. Get the size right before ordering, and note that a wider band fits tighter than a narrow one.
See also Chisel rings, Chisel stainless steel rings and all Rings.