Here's my two cents:
Nicotine: prevents aphid species and some caterpillar species. Add about 10-30 grams of tobacco to 1 litre of water. Let this boil for 10 minutes (yes! boil!) so you don't spread TMV onto your plants. This can be used as a mist or spray. Nicotine is toxic, but will easily be washed off by rain. Most insects have become resistant though, thanks to, who would've thought? Yes, Bayer. Another monopoly established.
Neem oil: add a teaspoon of oil to 2 litres of warm water. Add some biological soap as emulgator (dissolves the oil into the water). Use this as a spray. This'll help againt spider mite, thrips and aphids (allround spray).
Garlic: press about 5 cloves of garlic into a litre of water. Use this as a spray against lice/aphids.
Other ways are to plant some helpfull plants like garlic and tobacco, which act as a natural deterrent by chemical messaging.
Also I've read about some indians (those from India) who are using Pepsi. Don't know if that works though, but I'll give it a try whenever infestation time's here.