For the original recipe and instructions, see: "Pickled Red Onions" at foodfidelity.com
These will last for a few months, but of course they start to lose their flavor and crispness after a while, so I prefer to finish them in 1-2 weeks.
Only use glass or ceramic containers. Avoid metal which can react with the vinegar. Plastic is troublesome to given it absorbs flavors.
Whole spice seeds (peppercorns, pepper flakes, fennel seeds, etc.) are good ways to spice things up. Bay leaves add something as well
"A mere listing of ingredients is not protected under copyright law. However, where a recipe or formula is accompanied by substantial literary expression in the form of an explanation or directions, or when there is a collection of recipes as in a cookbook, there may be a basis for copyright protection."
On this site, for recipes written by others, the ingredients are listed and a link to the original recipe has been provided.