I've been a big proponent of Neem for years. Here's a chunk of wikipedia:
Usage
In India, the tree is variously known as "Divine Tree", "Heal All", "Nature's Drugstore", "Village Pharmacy" and "Panacea for all diseases". Products made from neem have proven medicinal properties, being anthelmintic, antifungal, antidiabetic, antibacterial, antiviral, anti-infertility, and sedative. It is considered a major component in Ayurvedic medicine and is particularly prescribed for skin disease[citation needed].
Neem twigs are used for brushing teeth in India, Bangladesh and Pakistan. This practice is perhaps one of the most effective early forms of dental care.
All parts of the tree (seeds, leaves, flowers and bark) are used for preparing many different medical preparations.
Neem oil is used for preparing cosmetics (soap, shampoo, balms and creams), and is useful for skin care such as acne treatment, and keeping skin elasticity.
Besides its use in traditional Indian medicine the neem tree is of great importance for its anti-desertification properties and possibly as a good carbon dioxide sink.
Practictioners of traditional Indian medicine recommend that patients suffering from Chicken Pox sleep on neem leaves.
Neem Gum is used as a bulking agent and for the preparation of special purpose food (those for diabetics).
Aqueous extracts of neem leaves have demonstrated significant antidiabetic potential.
[edit] Horticultural usages
Neem is a source of environment-friendly biopesticides. Among the isolated neem constituents, limonoids (such as Azadirachtin) are effective in insect growth-regulating activity. The unique feature of neem products is that they do not directly kill the pests, but alter the life-processing behavior in such a manner that the insect can no longer feed, breed or undergo metamorphosis.[3] However, this does not mean that the plant extracts are harmful to all insects. Since, to be effective, the product has to be ingested, only the insects that feed on plant tissues succumb. Those that feed on nectar or other insects (such as butterflies, bees, and ladybugs) hardly accumulate significant concentrations of neem products.
[edit] Uses in pest and disease control
Neem is deemed very effective in the treatment of scabies although only preliminary scientific proof exists which still has to be corroborated, and is recommended for those who are sensitive to permethrin, a known insecticide which might be an irritant. Also, the scabies mite has yet to become resistant to neem, so in persistent cases neem has been shown to be very effective. There is also anecdotal evidence of its effectiveness in treating infestations of head lice in humans. A tea made of boiled neem leaves, sometimes combined with other herbs such as ginger, can be ingested to fight intestinal worms.[4]
The oil is also used in sprays against fleas in cats and dogs.
The tender shoots and flowers of the neem tree are eaten as a vegetable in India. Neem flowers are very popular for their use in Ugadi Pachadi (soup-like pickle)[5] which is made on Ugadi day in South India. A soup like dish called Veppampoo Rasam (translated as 'juice of neem flower') made of the flower of neem is prepared in Tamil Nadu.
Neem is also used in parts of mainland Southeast Asia, particularly in Cambodia and Thailand (where it is known as sadao or sdao), Laos (where it is called kadao) and Vietnam (where it is called sầu đâu). Even lightly cooked, the flavour is quite bitter and thus the food is not enjoyed by all inhabitants of these nations, though it is believed to be good for one's health. Neem Gum is a rich source of protein.
I have one lone eggplant growing in a container on the porch. All other plants have died after producing nothing. 
