The total value of U.S. exchange traded funds rose $60.5 billion in April, a 5.7% increase from March, bringing the total value of ETF investments to more than $1.12 trillion, according to State Street Global Advisors.

Global, commodity and large-cap funds were particularly popular with investors last month as those three categories enjoyed monthly assets gains of 28.4%, 11.7% and 7%, respectively.

State Street's monthly snapshot report found that investors in April added more than $21.8 billion to ETFs than they withdrew, the eighth consecutive month of positive ETF inflows.

ETFs, which give investors an opportunity to buy indexed clusters of stocks or bonds or commodities but sell them on a daily basis just like a stock, continue to attract investors' interest and dollars.

In the last five years, ETF assets have grown at a compound annual growth rate off 27% a year and, through the first four months of 2011, they appear to be capable of meeting or existing that impressive growth rate this year, too.

Tom Anderson, global head of ETF strategy and research, notes that total ETF inflows have exceeded $100 billion a year in each of the last four years. With $50 billion-plus already added to the ETF pool in four months, it's clear 2011 is shaping to be another banner one for ETF funds, managers and investors.

"There are a number of reasons ETFs are so popular right now," Anderson said. "It really varies by investor. Some are active traders that are tactically allocating by a particular sector sectors. Some are buy-and-hold investors."

At the end of 2010, ETFs accounted for 11.2% of all assets invested in active funds compared to 12.3% in indexed mutual funds and 76.5% plowed into active mutual funds, Anderson said. In 2001, ETFs only accounted for 1.5% of these assets.

He added that roughly 40% of ETFs are purchased by institutional firms, 40% are bought by intermediaries and advisors and 20% -- give or take – are swooped up by retail investors.

"If you see a big move in one sector in a month, that's probably a result of big institutional flows," he said.

By manager, Blackrock still remains the head-and-shoulders leader with 222 ETFs at the end of April with more almost $500 billion assets. State Street checked in second with $257 billion in assets and Vanguard was third at $172 billion.

By sector, health care ETF assets rose 12.7% to just over $9 billion while energy and financial funds fell 4% and 3.1%, respectively.

The top U.S. ETFs by asset value at the April were SPDR S&P 500 ($95.2 billion), SPDR Gold Shares ($61.7 billion) and Vanguard Emerging Markets ($49.4 billion).