Which skin care products are scientifically proven to have an effect?

There are a lot of skin care products sold in the world and they all claim to be the next holy grail of youthful skin appearance.  So what products actually have clinical scientific studies behind them that back up their claims?

Of the topical skin care creams there are on the market, 3 products have decent levels of clinical scientific studies to support their manufactures claims of reducing fine lines and wrinkles:

Alpha Hydroxy acids - researches concluded that alpha hydroxy acids "produced a significant reversal of epidermal and dermal markers of photo aging."
 

Retinoic acid - research has concluded that Retin A (Retinoic acid) was found to reduce fine wrinkles and skin roughness, increase epidermal thickness and stimulate deposition of collagen.

Estrogens - Several studies indicate that postmenopausal women on estrogen replacement therapy develop less wrinkles and have better skin texture and elasticity than those not taking estrogens.