"I love Los Angeles. I love Hollywood. They're beautiful. Everybody's plastic, but I love plastic, I want to be plastic." -Andy Warhol

Most of us are aware of the mind boggling numbers of plastic bags that are consumed each year (in the ballpark of 500 billion to 1 trillion plastic bags, worldwide) and there has been great focus recently on not just recycling, but re-using. After all, recycling is still waste. That is to say, without eliminating the need for something (in this case, choosing reusable, cloth bags for all shopping instead of coming up with more uses for the plastic ones) one continues the production-consumption cycle. For the sake of sanity, let's assume the reusable cloth bag discussion is a done deal. So, beyond cleaning up after your dog and more grocery shopping, what more reuse can you get from that lovely pile of polymers at home?
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

Making pet pillows out of bags, etc(plastic bags as wrapping paper)