A while back, I saw that the Drinkhacker had reviewed a curious product called Spike Your Juice. I was so excited by it that I emailed their Customer Service on the product's website to see if they would send me a free sample to review, and they did. Because of their kindness and their great product, I will be ordering more soon with my own hard-earned money.
Spike Your Juice is a small kit that contains all you need in order to begin making your own cider or wine at home. The kit comes with a bubbler airlock that will fit on most large commercial 64oz juice bottles, six packets of yeast, and a bunch of quaint labels to put on your homemade hooch once it's done.
The process to make your own booze with this kit is simple and fun. You take a bottle of your favorite kind of juice, pour in a packet of yeast, plug the bottle with your bubbler airlock filled slightly with water, and wait! The yeast immediately begin consuming the sugar in the juice and begin emitting alcohol and carbon dioxide as waste... delicious, delicious waste. Within 8 hours you can see many tiny bubbles rising to your juice's surface while your airlock lets out excess gas and keeps out bacteria. If you didn't have an airlock, your capped bottle would explode in a matter of hours.
As a side note, it turns out the the Spike Your Juice yeast packets are in fact yeast and a bit of sugar mixed in. It may be the added sugar or that it's a particularly fast kind of brewing yeast, but the effects of the yeast's consumption can be seen hours quicker than if you used a simple run-of-the-mill yeast from your grocery store... I experimented and confirmed it.
The fermenting will stop when either 1) you put the bottle in the fridge to chill and kill the yeast (but cap it loosely if your airlock doesn't fit in the fridge!), 2) you drink it, 3) there is no sugar left for the yeast to consume, or 4) when the alcohol-by-volume of the juice reaches about 14%, which is an environment that naturally kills off the yeast. But watch out, if you let it ferment much past 48 hours, most of the juice's sugar will be consumed by the yeast, and your juice/hooch will no longer be very sweet.
This stuff is great fun. The first thing I fermented was Welch's Concord Grape juice, a product on Spike Your Juice's recommended juice list(pictured right). After 48 hours, the juice was carbonated, still sweet, and slightly boozy. The yeast lend a pungent flavor to the juice, which is tolerable, but not ideal. I found that running the juice through a coffee filter can remove most of the yeast (taste)... also another way to slow down the fermentation.
After I tested a recommended juice, I set out to try it on my own favorites... and I learned a valuable lesson: carefully check your juice's ingredients list before you try to ferment. It goes without saying that yeast will only consume natural sugar and not artificial sweetener, but another aspect to consider is preservatives. I wanted nothing more than Hawaiian Punch wine, but it is not to be; after the yeast floated in the punch for a day, I realized that (with the help of my friend who's a doctoral biology student) the culprit is the punch's Potassium Sorbate, a preservative which is specifically used for killing yeasts and molds. Whoops.
So far I've fermented grape juice, apple juice, cranberry cocktail, fruit punch, (bottled, non-refridgerated) orange juice, and a big jug of apple cider. I brought the fermented cider to Thanksgiving, and it was a hit (pictured below).

I highly recommend this product. It's cheap($10), simple, educational, and a lot of fun. You can turn your favorite juice into a wine or cider and enjoy it in a different and novel way.
Experiment responsibly!
Experiment responsibly!