The rich got quite a bit richer this past year, according to this year's rankings of the 400 wealthiest Americans. Forbes magazine released its annual list on [September 19], and the combined net worth jumped 13% to $1.7 trillion in 2012, up from $1.5 trillion in 2011. The boost came thanks to the rising stock market and a rebound in real estate values - especially in cities like Los Angeles and New York. Microsoft founder Bill Gates remained at the top of the list, as his net worth rose $7 billion to $66 billion. His pal Warren Buffett, CEO of Berkshire Hathaway, also saw his net worth climb by $7 billion, which helped him retain the number two spot on the list with $46 billion. Another software mogul, Oracle CEO Larry Ellison, enjoyed the biggest increase in wealth of anyone on the list -- a jump of $8 billion. That put his net worth at $41 billion, ranking him No. 3 on the list. The average net worth of a member of the Forbes 400 hit $4.2 billion. That's the highest level it's been in at least a decade, according to the magazine, and up from $3.8 billion last year. The net worth cut off to make the list this year was $1.1 billion. Forbes said that 241 members of the 400 enjoyed an increase in their net worth, while only 66 members suffered a decline.