Plastics come in seven different varieties, numbered 1-7 on the bottom of the packaging, within the triangular recycle symbol. These plastics have a variety of different recycling capabilities, as well as different chemical compositions, some of which are harmful.

Avoid Plastics 3, 6 and 7.
Instead choose Plastics 1, 2, 4 and 5.

Plastic 1 (PETE): Recyclable and generally safe.

Plastic 2 (HDPE): Recyclable and generally safe.

Plastic 3 (PVC): Avoid this plastic whenever possible! It is made with polyvinyl chloride which can leach lead and phthalates that harm hormones. It releases carcinogenic dioxins into the environment and food, and often contains lead.
When possible choose non-PVC cling wrap, such as Glad and Handiwrap brands.

Plastic 4 (LDPE): Plastic four is one of the safer plastics, as it is not know to contain hazardous chemicals.
This type of plastic is usually used for plastic bags--both shopping bags and ziplock-type bags. These can be washed and reused until they start to look cloudy--this is a sign of deterioration, at which point the plastic becomes potentially harmful. Many grocery stores such as Whole Foods will recycle plastic 4, which is usually not recyclable through curbside recycling programs. Some stores only take grocery bags, but others take frozen-vegetable bags, cling wraps and plastic produce bags. When recycling make sure the plastic is clean and dry, or it can ruin the entire plastic melt.

Plastic 5 (PP): This plastic is made from polypropylene, and is one of the safer plastics to use with food. Many tupperwares are made from plastic 5. This type of plastic is not known to leech chemicals, and is not made with chlorine. Unfortunately, it is not commonly recyclable.

Plastic 6 (PS): This plastic is known to leech chemicals that disrupts hormone functions, and is generally not recyclable. Plastic 6 should be avoided when possible.

Plastic 7 (Other): This plastic is never recyclable, and contains bisphenol A (BPA). This plastic should be avoided when possible.


Additional Information:
-Plastics 1 and 2 aren't recycled into plastic packaging, but rather textiles, parking lot bumpers, and plastic lumber--all unrecyclable products. Because of this recycling does not reduce the use of virgin materials. Instead, the material is only temporarily diverted from landfills.
-Avoid using plastics in the microwave.
-BPA, found in many plastics, is not known to cause cancer. However, it does affect hormones that protect against heart attacks and Type II diabetes.
-Most cling-wrapped meats and cheats are wrapped in PVC--immediately remove them from their original packaging when purchased.
-The arrow symbol does not mean a product is recyclable! The useful information comes from the number inside the arrows.
-Plastic resins are made from a non-renewable natural resource that could be used elsewhere or saved.
-Plastic doesn't save energy--it is just as energy consuming to make as glass, and much more consuming than recycled glass. Also, recycling plastic is expensive, both in capital investment and energy use.
-The best way to reduce plastic consumption is to reduce its demand--avoid purchasing plastics whenever possible!

Solutions:
-Avoid single use, disposable packaging.
-Bring cloth bags to the grocery store.
-Buy in bulk--it reduces packaging.
-Choose refillable containers--preferably glass and steel.
-Bring your own container to coffee shops, frozen yogurt and ice cream shops, etc.


The Green Guide has a great reference list for plastics to avoid and which ones to choose instead, including brand names.