Lime

In my kitchen, the most ingredient for me is "Lime". Because of I love sour taste recipes, this ingredient is very necessary for me... Tom Yam Kung (Sour soup), Som Tam (Papaya Salad), fried rice etc., lime juice is needed for these...

In addition, lime was used as herb. My mother and I take the lime juice with honey for the good excretory system.
Lime is a term referring to a number of different fruits (generally citruses), both species and hybrids, which are typically round, green to yellow in color, 3-6 cm in diameter, generally containing sour pulp, and frequently associated with the lemon. Limes are often used to accent the flavors of foods and beverages.

Varieties
The most commonly available commercial limes (or Limon) are the larger, greener Persian lime (Citrus latifolia) and the smaller, yellower Key lime (Citrus aurantifolia) (also known as the Mexican Lime). "Key lime" is an American retronym, as the original fruit known in English as a "lime" was Citrus latifolia, derived from the Persian name, limu (the fruit was introduced to Europe during the Crusades).

Other lime varieties include :
Mandarin lime (Citrus limonia)
Kaffir lime (Citrus hystrix)
various Australian limes
Sweet lime (Citrus limetta)
Palestine sweet lime (Citrus limettioides)
and musk lime (X Citrofortunella mitis).

Uses

For Drinks:
Lime fruit, and particularly their juice, are used in beverages, such as limeade (akin to lemonade). Alcoholic beverages prepared with limes include cocktails such as gin and tonic, margarita, mojito, Caipirinha and Cuba libre, as well as many drinks that may be garnished with a thin slice of the fruit or corkscrew strip of the peel (twist). One customary consumption of tequila is in shots accompanied by lime wedges and salt. Beer is often served with limes in Mexico. Lime juice is the primary ingredient of Bonji Water, a popular drink in southern parts of Kerala, India. Lime juice is also used in some commercial soft drinks.

Lime juice is made into sirup and sauce and pies similar to lemon pie. "Key Lime Pie" is a famous dish of the Florida Keys and southern Florida, but today is largely made from the frozen concentrate of the 'Tahiti' lime.

Mexican limes are often made into jam, jelly and marmalade. In Malaya, they are preserved in sirup. They are also pickled by first making 4 incisions in the apex, covering the fruits with salt, and later preserving them in vinegar. Before serving, the pickled fruits may be fried in coconut oil and sugar and then they are eaten as appetizers.

For Cooking:
In cooking, lime is valued both for the acidity of its juice and the floral aroma of its zest. It is used in Key lime pie, a traditional Florida dessert, and is a very common ingredient in authentic Mexican, Southwestern United States and Thai dishes. It is also used for its pickling properties in ceviche. Additionally, the leaves of the Kaffir lime are used in southeast Asian cuisine. The use of dried limes as a flavouring is typical of Persian cuisine. Limes are also an essential element in Tamil cuisine.

For other uses:
Juice: In the West Indies, the juice has been used in the process of dyeing leather. On the island of St. Johns, a cosmetic manufacturer produces a bottled Lime Moisture Lotion as a skin-conditioner.

Peel: The dehydrated peel is fed to cattle. In India, the powdered dried peel and the sludge remaining after clarifying lime juice are employed for cleaning metal.

Peel oil: The hand-pressed peel oil is mainly utilized in the perfume industry.

Twigs: In tropical Africa, lime twigs are popular chewsticks.

Medicinal Uses:
Lime juice dispels the irritation and swelling of mosquito bites.

In Malaya, the juice is taken as a tonic and to relieve stomach ailments. Mixed with oil, it is given as a vermifuge. The pickled fruit, with other substances, is poulticed on the head to allay neuralgia. In India, the pickled fruit is eaten to relieve indigestion. The juice of the Mexican lime is regarded as an antiseptic, tonic, an antiscorbutic, an astringent, and as a diuretic in liver ailments, a digestive stimulant, a remedy for intestinal hemorrhage and hemorrhoids, heart palpitations, headache, convulsive cough, rheumatism, arthritis, falling hair, bad breath, and as a disinfectant for all kinds of ulcers when applied in a poultice.

The leaves are poulticed on skin diseases and on the abdomen of a new mother after childbirth. The leaves or an infusion of the crushed leaves may be applied to relieve headache. The leaf decoction is used as eye drops and to bathe a feverish patient; also as a mouth wash and gargle in cases of sore throat and thrush.

The root bark serves as a febrifuge, as does the seed kernel, ground and mixed with lime juice.

In addition, there are many purely superstitious uses of the lime in Malaya.

Plants known as "lime"
Australian limes
Australian desert lime (Citrus glauca)
Australian finger lime (Citrus australasica)
Australian round lime (Citrus australis)
Blood lime
Kaffir lime (Citrus hystrix) (a.k.a. kieffer lime; makrut, or magrood)
Key lime (Citrus aurantifolia) (a.k.a. Mexican, West Indian, or Bartender's lime)
Mandarin lime (Citrus limonia)
Musk lime (X Citrofortunella mitis)
Palestine sweet lime (Citrus limettioides)
Persian lime (Citrus x latifolia) (a.k.a. Tahiti or Bearss lime)
Spanish lime (Melicoccus bijugatus) (a.k.a. mamoncillo, mamn, ginep, quenepa, or limoncillo) (not a citrus)
Sweet lime (Citrus limetta) (a.k.a. sweet limetta, Mediterranean sweet lemon)
Wild lime (Adelia ricinella)
Limequat (lime kumquat)
Lime tree (Tilia sp.)

Ref : http://en.wikipedia.org, and http://www.hort.purdue.edu