They pledged a total of $1.1 trillion (£681bn) in funding to tackle the crisis, including $750bn to the International Monetary Fund, $250bn to boost global trade and $100bn for international development banks to lend to the poorest countries.
Leaders also agreed to introduce tougher financial regulations and sanctions against secretive tax havens.
"This was the day the world came together to fight back against global recession," said Gordon Brown, the host of the summit.
Representatives from the developing world welcomed the outcome.
Brazilian President Luiz Inacio Lula da Silva told the BBC's Newsnight programme that rich countries had engaged with emerging nations on "equal terms" to achieve a good result.
French President Nicolas Sarkozy - who had threatened to walk out of the meeting if it did not yield concrete gains - said that the conclusions were "more than we could have hoped for".
He will meet Mr Obama for one-to-one talks on Friday, after which the US leader will cross into Germany for a meeting with Chancellor Angela Merkel.
Then the focus will turn to Nato and the 60th anniversary summit that is being hosted jointly by France and Germany.
Leaders will gather for a working dinner in the German city of Baden Baden on Friday night before the main talks on Saturday.
The US president is expected to use the opportunity to build support for his new strategy for Afghanistan.
More troops are needed certainly, says the BBC's diplomatic correspondent Jonathan Marcus, but above all the Americans want to see their allies stumping up a good deal more money and more training teams to build Afghanistan's own security forces.
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