Bill Gates is once again No.1, followed closely by investor Warren Buffett. Google founders made the list on their company IPO.

NEW YORK (CNN/Money) - Bill Gates can now breathe a sigh of relief.

The founder of Microsoft Corp. (MSFT: Research, Estimates), the world's largest software maker, is still the richest man in America, according to Forbes magazine's annual list of the 400 richest Americans released Thursday.

For the first time since 2000, the magazine said, "the combined net worth of the nation's wealthiest climbed to $1 trillion, up $45 billion in 12 months." A record number of billionaires--313--was instrumental in reaching the trillion-dollar mark.

Gates' estimated wealth rose to $48 billion from $46 billion in 2003, followed closely by billionaire investor Warren Buffett with $41 billion. But the magazine said Gates' net worth did not include the $28 billion he gave away to charities over the past years. Otherwise, his combined assets could top $76 billion.

Buffett, nicknamed the "Oracle of Omaha," was the biggest dollar gainer on the list with a $5 billion net increase, Forbes said.

Paul Allen, Microsoft's co-founder, stood at No. 3 with $20 billion, down $2 billion from 2003.

Members of the Walton family, whose fortune comes from Wal-Mart Stores Inc. (WMT: Research, Estimates), took the next four spots each with an estimated wealth of $18 billion, according to Forbes.

Michael Dell, founder of Dell Inc. (DELL: Research, Estimates), and Larry Ellison of Oracle Corp. (ORCL: Research, Estimates) stood at the No.9 and No.10 spots respectively.

But tech recovery failed to revive fortunes for everybody. The magazine said Jeff Bezos, founder of Amazon.com (AMZN: Research, Estimates), is the biggest money loser remaining on the list. Bezos dropped two spots to 38 and lost $800 million over the last 12 months.

Forbes said 45 new members joined the list this year, including Google's Larry E. Page and Sergey Brin, who is also the youngest member of the Forbes 400 at age 31. The two Google (GOOG: Research, Estimates) founders tied for No. 43 with $4 billion each, after their online search engine went public in August.

One of the most prominent returnees on the list might be first-lady hopeful Teresa Heinz Kerry, whose inherited fortune from her late husband is estimated at the list minimum of $750 million, the magazine said.

And despite financial troubles at his casino and hotel business, Forbes said real estate mogul Donald Trump's net worth rose $100 million to $2.6 billion. But his ranking dropped 3 spots to 74.

Forbes also said the combined net worth of America's wealthiest reached $1 trillion for the first time since 2000, up $45 billion the past 12 months alone.

There are now 313 billionaires in America, up from 262 counted last year; it's the largest number of billionaires ever on the list, the magazine said.

The list shows California has the most resident members with 98, twice the number of the New York state, which has 49. But New York City still has the most 400 list members per city with 38, followed by San Francisco with 22 and Los Angeles with 19.