Real Simple mag has a listing of great uses that I recommend checking out, some of which include plastic bags as knee pads for cleaning or gardening, over-the-hand for handling raw meats, and making parachutes for action figures.
For the crafty ones who might like to fashion their own bag-dress, check out Plastic bag crafts post on the Craftzine.com blog.
Resealable bags can be washed and reused (if you can get your family to bring them home). They even sell a handy dandy bag drying rack:
But my cheap-self constructed the poor-girl version (which is pretty sad since the gizmo runs about $15) made of a mug filled with rice or beans and a dozen chop sticks:
I reuse most tortilla bags, bread and deli bags for all our weekly lunch packing. Plastics are one of the most sturdy man-made materials, which makes it a shame to not consider alternative uses for more than just bags.
When cleaned and stored properly, your plastic (or glass) peanut butter bottle has a lifetime of uses. Mine live in the pantry and garage, storing bulk foods and loose nails and screws.
I found a post on thriftyfun.com for alternative uses for laundry detergent bottles, but they were a little too much for even me. My favorite use, locally, is to take the old bottle on down to Earth Goods General Store and re-fill it.
For information on the safety of specific plastics, reuse, and storage, I suggest checking plasticsinfo.org, then backchecking it with The Environmental Working Group (search: 'plastic safety') who, independently, researches claims of safety made by the FDA, EPA, and other regulatory agencies. Get the facts and make the best decision for you.
here is a list of some other websites with extensive lists for plastic bag uses:
Rustic Girls have some chic ideas
61 uses for Wal-Mart bags