According to the National Stock Exchange, the combined assets of all U.S. exchange-traded funds were $534.58 billion at the end of 2008. This figure represents around a 13.5 percent decline from 2007 when ETF assets ended the year at $617.73 billion.

Despite the fall in ETF assets under management, investor demand for these low-cost index funds hasn’t subsided. The net cash flow in ETFs climbed to $178.39 billion last year from $149.02 in 2007.

The bulk of ETF assets are in just a handful of funds like the SPDRs S&P 500 (SPY), the iShares MSCI EAFE Index Fund (EFA) and the Vanguard Total Stock Market ETF (VTI). Together, these funds alone account for $135 billion or just over one-quarter of all ETF assets.

At the close of 2008, there were 758 ETFs and 90 ETNs.