The main premise behind whitening products is to slow down the melanin production, preventing skin darkening. Besides this, most of the skin whitening products are chemical exfoliants, which means that they have the potential to induce mild skin peeling, thus facilitating the development of fresh and brighter skin layer.
The results will clearly vary from brand to brand, due to different chemical compositions, but the result aims to lighten the skin, including your overall shade and lightening individual dark spots. Most brands will include a small amount of Glutathione and/or Alpha Hydroxy Acid. Both chemicals are safe for use on the skin, but due to strict FDA regulations, high percentage products cannot be sold as cosmetic products on the shelf.
When it comes to the availability of products, North Americans are at a great disadvantage seeing as we can't exactly pop into our local Sephora and stock up on Japanese-blend Shiseido (the shiseido whitelucent line sold in north america is a disaster in comparison to the asian blend, but thats for another post). Asian brands are years ahead the skincare game, with proven safe results.
My personal preference, Korean cosmetics. If you're curious and want to try a cheap but decent whitening cream, Skin79 would be a great place to start (try the White Reviving Skin Radiance Cream, great results in just a few weeks).
With whitening creams, there is a very broad spectrum when it comes to price point. Anything from the Hada Labo Shirojyun Ultimate Whitening Series, especially the whitening essence is easily the cheapest, to $1050 La Prairie creams. Honestly, a whitening cream should not be the cheapest part of your skin care routine, but it also should not break the bank. A happy medium could be the anything from the Guerlain blanc de perle line, especially the serum.
My favorite cream? Shiseido Vital-Perfection Science Cream AAA, extremely hard to find, but nothing gives results like this.
the holy grail