How about the 'Miracle Berry', a berry, that, when eaten before meals, makes sour food taste sweet! this is an entry from wikimedia.org, one article
on its controversial history in respect with research/approval, and another on its properties. From
Wikimedia.org on miracle berry
An attempt was made in the 1970s to commercialize the ability of the fruit to turn non-sweet foods into sweet foods without a caloric penalty, but
ended in failure in controversial circumstances with accusations that the project was sabotaged and the research burgled by the sugar industry to
prevent loss of business caused by a drop in the need for sugar. The FDA has always denied that pressure was put on it by the sugar industry, but
refused to release any files on the subject. Similar arguments are noted for FDA's regulation on stevia now labeled as a "dietary supplement"
instead of a "sweetener".
Recently, the fruit has become popular in Bacchanalian-like food tasting events, referred to as "flavor tripping parties" by some. The tasters
consume sour and bitter foods, such as lemons, radishes, and beer, to experience the taste changes that occur. A blog dedicated to the phenomenon of
"flavor tripping" describes the miracle fruit "like a candy Willy Wonka would have invented." 
'The Miracle Fruit plant produces berries that, when eaten, cause bitter and sour foods (such as lemons and limes) consumed later to taste sweet. The
berry, also known as Miracle Berry, Magic Berry, or Flavor Berry (Sideroxylon dulcificum/Synsepalum dulcificum) was first documented by explorer
Chevalier des Marchais during a 1725 excursion to its native West Africa. Marchais noticed that local tribes picked the berry from shrubs and
chewed it before meals. The plant grows in bushes up to 20-feet high in its native habitat, but does not usually grow higher than ten feet in
cultivation, and it produces two crops per year, after the end of the rainy season. It is an evergreen plant that produces small red berries, with
flowers that are white and which are produced for many months of the year. The seeds are about the size of coffee beans.
The berry contains an active glycoprotein molecule, with some trailing carbohydrate chains, called miraculin. When the fleshy part of the fruit is
eaten, this molecule binds to the tongue's taste buds, causing bitter and sour foods to taste sweet. This effect lasts between thirty minutes and two
hours. It is not a sweetener, as its effects depend on what is eaten afterwards, but has been used to cause bitter medicine to taste sweet.'
[edit on 15-7-2008 by star in a jar]