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…).

By all accounts the storm that hit New York’s Central Park last week didn’t last very long, but the devastation was breathtaking. In a matter of minutes, winds approaching hurricane-strength flattened hundreds of old beloved trees and damaged hundreds more. With roots in the air and limbs askew, and the dead and wounded strewn everywhere, the soft green heart of this hard gray city had taken a direct hit. The days that followed were filled with the cracking of ripped timber, the whine of power saws and the relentless buzz of wood-chippers. Grass will grow where giants once stood. Sunlight will filter down to the urban forest floor for the first time in years. New trees will be planted. And in a few decades, incredibly, no one will be the wiser.

Central Park, after all, was never the forest primeval. Still, there is something sacred about old trees – even if their age is measured in decades rather than centuries, and their arrangement determined by a landscape architect. They grew up with us, or we with them. In a place of constant change they are, simply, constant. If trees can be so easily uprooted, what chance have we? It is unnerving to see how shallow and vulnerable a tall tree’s roots really are.

It was a wonderful little bubble while it lasted. Getting up before dawn. Dressing in easy-to-peel layers for whatever the day might bring. Walking over to Boynton-McKay, a diner of rare perfection, where the wi-fi was as reliably good as the pancakes (a boon in connectivity-challenged Camden…) Ascending the stairs and more stairs of the town’s famous 19th century Opera House. A few minutes to mingle-navigate among tables of nibble-food before settling down for a morning of things worth thinking about.

But first, a little music. Logan Richardson’s soulful, playful, questioning sax riffs on “America the Beautiful” one day. Zoe Keating’s clear, deeply layered, architecturally precise, transcending cello pieces another. How lovely to start each day by notthinking. Just being. In the moment. Together. Brilliant.

And then it was off and running, from economics to education, urban decay to urban agriculture, environmental catastrophe to conservation hope, design theory to food design, cardboard robots to paper diagnostics, communications to comics, art to dance to music. To, to, to…

The next agricultural revolution will not be patented. It will not depend on genetically modified seeds or petrochemical fertilizers. It will not poison or deplete aquifers. It will not erode topsoil that took millennia to form. Nor will distance between “farm and fork” be measured in thousands of gas-guzzling miles.

The next agricultural revolution won’t even take place on the farm – at least as we know it.

It will be potted and stacked, set up in hoop houses and warehouses, sprout from rooftops, vacant lots and lawns. Worms will be celebrated, bacteria will flourish and grubs nurtured. It will be drought and flood resistant and productive all year long.

The next agricultural revolution will be street-smart and urban, yet mimic nature far more closely than agro-giant operations sprawled over hundreds or even thousands of monotonous monoculture acres.

Best of all, the next agricultural revolution is well underway, just 5 blocks from Milwaukee’s largest public housing project, off a busy street, behind an unassuming farm-stand surrounded by sunflowers basking in the brilliant light of a mid-September afternoon. Welcome to Growing Power.

Hope Phones is one of those “Gosh, yes!” ideas:

• Get people to donate old cell phones to a recycling company
• Get recycling company to assign each phone a value
• Use value to trade for refurbished phones
• Donate refurbished phones to clinics in developing countries to use for sending health-related text messages
• Good begets good

Stanford student Josh Nesbit, who came up with the scheme, spent last summer at a tiny hospital in rural Malawi armed with 100 refurbished phones ($10 per), a used laptop and some free software called FrontlineSMS for managing text messages. Could he set up a phone network to deliver more and better health care to the 250,000 people living in the region served by the hospital?

I knew I’d seen that face before. Those cheeks. Those whiskers. That long, long tail. The giant African pouched rat, a.k.a. the giant Gambian pouched rat (Cricetomysgambianus), was all over the headlines five years ago, fingered as the likely culprit in a first-ever outbreak in the U.S. of monkeypox (a smallpox relative).

Shift continents and the villain becomes a hero. In fact, a “HeroRAT,” with a genius for sniffing out landmines and diagnosing TB.

As part of Popular Mechanics magazine’s annual conference on world-changing innovation, Amy B. Smith, MIT’s pied piper of Design-That-Makes-a-Difference, was named this year’s Breakthrough Leadership award-winner. It was an easy choice. Smith and her team of “D-Lab” students have helped set the bar for practical brilliance. Whether they are making charcoal from plant waste or engineering a better corn-shucker, it is thrilling to see the dramatic impact their simple yet deft solutions to grinding every day problems can have on people’s lives.

Even those of us best described as “mechanically-challenged” can grasp how these inventions work — which is a big part of the point. In fact, it is #4 on Smith’s list of“Seven Rules for Low-Tech Engineering”: