Native to tropical parts of Mexico and Central America, poinsettias were well-known to the Aztecs before being brought north by Joel Poinsett, the American Ambassador to Mexico. Today, with their lush green and brilliant red, poinsettias are the quintessential Christmas plant — and post-Christmas compost. But it needn't be! Poinsettias make great houseplants, and with a little diligence you can even get them to rebloom next year.
If you live in Zones 9-12, you can even plant your poinsettia outside. Here in Oakland, there are twelve foot poinsettia shrubs tucked in sunny, sheltered corners all over the place. Poinsettias like moist, well-drained soil and need to be protected from frost. Choose a full-sun location against a wall (which will absorb and radiate the sun's warmth) or in an otherwise protected corner. The bloom cycle of a poinsettia is triggered by day length, so happily they'll still bloom right at Christmas!
If you live in an area with a harsher winter, don't despair! Poinsettias also make wonderful houseplants. Use good potting soil, the occasional fertilizer if you like (I use osmocote so I can fertilize once and forget about it), and water when the top inch is dry. Place your poinsettia in the sunniest, least drafty spot in your house. When the outdoor temperatures are reliably over 60°F, including at night, move it outside. Bring it back in late summer before temperatures drop again.
Here's the one slightly tricky part: to rebloom your poinsettia for late December, you'll have to put it in a closet every night starting in late September. Yes, a closet, or box, or any other place that gets no light. Absolute zero — even streetlights can mess it up. Ideally you want the poinsettias to have twelve hours of total darkness per day. In the past I've just associated poinsettia moving with feeding my cat. Out at breakfast, in at dinner.
And speaking of pets, while poinsettias are indeed toxic, they aren't as poisonous as they're hyped up to be.
For more information on poinsettias, and a great diagram on their yearly care, check out Michigan State University's page on the care of poinsettias.