According to a new study by Network for Good and True Sense Marketing, 20% of all online giving takes place in the last 48 hours of the year. So get out your laptops and cell phones, it’s time to dig into your cyber pockets and spread some love around.

There are plenty of ways to do it, too. This year’s digital darling, Groupon, has teamed up with crowdfunded microfinance pioneer Kiva to make your philanthropy dollars go further: 40% further. The coupon site is selling $25 donations for $15, with Groupon and its sponsors making up  the $10 difference up to $500,000, Kiva isn’t out a dime. The deal ends, along with 2010, on December 31.

Groupon competitor, Living Social, has a somewhat more complicated offer going with Global Giving, involving percentages of sales, a processing fee, benefiting five charities in Canada, the U.K. and Australia. Today it the last day, so we should know son how well it worked out.

No matter how you send in your dollars (credit card, text, check or “old timey“* coin in a kettle), be sure to use Charity Navigator to make sure an organization is as worthy as its cause.

There are plenty of worthy causes, too. But if you’re stuck, New York Times columnistNicholas Kristof has a few suggestions for lesser-known groups that could use some help (btw, no holiday required—give early, give often…).

The ancient alchemists aimed low, merely attempting to turn lead into gold for personal gain. The real magic, according to the chemists at start-up Micromidas , may be both muckier and microbial: turning sludge into bio-degradable plastic. If they are right, and their scheme scales commercially, it will be a win for everyone. What was once a problem will be transformed into an asset as a (literal) waste stream becomes a valuable feedstock. What was a  municipal cost will become a source of municipal income. And throw-away products made from eco-friendly plastic will, actually, goaway, decomposing into environmentally compatible parts, instead of swirling into eternity in middle-of-the-ocean gyres.

It is a radical re-think of the “extractive economy,” notes Ryan Smith, Micromidas’ CTO. After a few centuries of hauling finite resources—from fossil fuels to rare earth minerals—out of the ground, we have enough on the surface to keep us going, and in fairly good style, but only if we refocus our collective tech smarts and investment dollars on mining garbage.

Drilling for oil and refining it into a form that can be used to make a plastic bottle, for example,  is a long, complicated giant-carbon-footprint process. When the bottle is tossed, the energy embedded in its manufacture is lost as well.