Exchange-traded funds have been around since the early 1990s, but this is the year they've really arrived.

So far in 2000, the number of exchange-traded funds, or ETFs, has exploded, thanks in no small part to

Barclays Global Investors

. At the beginning of this year, there were 30 of these tradable funds. But Barclays alone has more than

doubled that number by launching about 35 brand-spanking-new exchange-traded index funds, called


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Unlike traditional mutual funds, the shares of ETFs are priced throughout each trading day and trade just like stocks. Most conventional mutual funds are priced once a day at the close of trading. This frequent pricing, coupled with lower costs, has made these tradable funds a very attractive alternative to index funds. ETFs now command more than $50 billion in assets.

Some of the new Barclays iShares haven't been all that popular. The

iShares Dow Jones U.S. Consumer Cyclical Sector

(IYC) - Get iShares U.S. Consumer Services ETF Report

index fund, for example, has just $15 million.

Still, investors now have a much wider array of choices than they used to -- from ETFs with a pointed sector focus to offerings tied to a broad market index. And with even more options on the way, more money will surely be flowing into these tradable funds. As the ETF performance chart below indicates, there's already plenty from which to choose.