Safety 
Studies by the USDA have found that more than 80% of celery, peach, and apple samples contained pesticide residue even when prepared for normal use by washing, peeling or coring. [12 different carcinogens and 17 different neurotoxins]
According to data from the USDA, more than 93% of conventional apples tested positive for organophosphate pesticides, which are nerve agents that studies have linked to decreased intelligence and increased attention problems in children. [Pediatrics, vol. 118, no. 6]
A study by the Consumer Report found 75% of conventionally grown produce had pesticide residue.
The EPA lists 65 pesticides used on food crops as possible carcinogens. Genetically modified foods may pose serious health and environmental problems. 85% of all soy is now grown from GMO seeds, 40% of all corn and 75% of all canola, to name a few. Since labeling is not required in the U.S., the only way you can be sure you are not buying GMO food is to buy certified organic food.
Nutrition
Organic food is more nutritious than conventionally grown food according to many recent studies. Organically grown vegetables tested were found to average 27% more vitamin C, 23% more iron, and 29% more magnesium than their conventionally grown counterparts. [reported in Nutrition Science News]
The Journal of Applied Nutrition study found the mineral content in organic produce approximately twice as high as conventionally grown produce. Another study found organic oranges to have 30% more vitamin C. Organically grown plants have a stronger immune system to protect themselves. (Chemically grown plants depend on the chemicals so do not develop as strong an immune system).
Remarkable differences are showing up between organically and conventionally grown produce in research being done at the University of California at Davis. For example, organic tomatoes had 97% higher flavonoids than conventionally grown tomatoes.
According to a recent study led by Newcastle University and funded by the European Union, organic milk contains 60% more antioxidants and desirable fatty acids than conventional milk.
Environment
Growing organically reduces toxic agricultural chemicals in our air, soil and water. This reduction contributes to a healthier environment for all people and wildlife. Support organic!