With the vast array of exchange traded funds (ETFs) to choose from, they continue to remain attractive, and for good reason. But that doesn’t mean you shouldn’t do your due diligence when choosing funds for your portfolio.

At the end of August, there was $674 billion in 858 U.S.- listed ETFs. One of the main reasons they’ve exploded in popularity is because they offer many investor-friendly characteristics:

Despite scrutiny by the as the Commodity Futures Trading Commission (CFTC), which was investigating possible causes of the wild volatility and surge in oil and gas prices last year, commodity exchange traded funds (ETFs) continue to grow in number and assets.

One of the most well-known commodity ETF providers, U.S. Commodity Funds, especially felt the wrath of the CFTC when two of their commonly traded funds, United States Natural Gas (NYSEArca: UNG) and United States Oil (NYSEArca: USO) came under the microscope. The primary reason these funds were looked at was concern that the growing popularity of futures-backed commodity ETFs were causing the volatility in oil and gas prices, leading to a huge surge in prices last year, states Max Frumes of Medill Reports. (How to play commodity ETFs).

ETF Spotlight on iShares Dow Jones U.S. Oil & Gas Exploration Index (NYSEArca: IEO), part of a weekly series. Assets: $280 million

Holdings: The holdings in this fund consist of 60 companies involved in the exploration and production of oil and gas in the United States. Among the top components include: Chesapeake Energy (NYSE: CHK), Occidental Petroleum (NYSE: OXY) and Valero Energy (NYSE: VLO).

Reflecting the rapidly growing popularity of emerging markets, iShares has filed for two new sector ETFs focusing on the asset class.

iShares has filed with the Securities and Exchange Commission (SEC) to launch the following ETFs:

The Dow Jones Industrial Average, or simply the “Dow,” does not indicate the state of the economy and it does not indicate the state of the stock market. So, why do we care about it?

The Dow is the average of the value of one share each of 30 of the largest companies in the United States, writes Trent for The Simple Dollar.

Stronger-than-anticipated industrial numbers from China had a nice side effect for Brazil and its related ETFs: it heightened investor risk appetite

Chinese factory output growth surged to a 19-month high in October. China, the world’s third-largest economy and a voracious commodities consumer, is widely considered a driver in a global economic recovery, reports Luciana Lopez for Reuters. The numbers gave investors the confidence they were seeking to move toward greater emerging market risk.

Certain types of investors are always on the lookout for a nice dividend yield in their domestic holdings. Did you know that handsome yields can be found in international ETFs, as well?

International dividend ETFs can provide decent yields and remove the need to do research on foreign stocks. Instead of trying to pick foreign holdings on limited information, there are funds that have pulled together some high-quality, dividend-paying companies that you can hold in a basket, thus spreading out the risk.

Van Eck, the provider of one of the top-performing gold-focused ETFs this year, has launched a new fund today targeting the small- and mid-cap gold mining companies.

Junior Gold Miners ETF (NYSEArca: GDXJ) is the latest fund from Van Eck. The index gives exposure to small- and mid-cap companies that derive at least 50% of their revenues from gold or silver. The smaller mining companies that are featured in the index may have greater volatility and risk because of their size. On the flip side, there’s plenty of potential for growth in these smaller companies. It’s also worth noting that small- and mid-caps tend to do better in recovery periods, since they’re more nimble and quick to adapt as economic conditions shift.

The BRICs (Brazil, Russia, India and China) have gotten the majority of investor attention, but there are other worthy emerging market ETFs that lie outside their boundaries.

Many countries that fall under the emerging and or frontier market categories get overlooked, overshadowed by the BRIC wall. Some analysts say if you’re not looking at some other markets, you could be leaving a wide-open hole in your portfolio.

As we take a moment to reflect on the past year, it becomes obvious that the housing market bust crippled the economy. What made this cyclical bust in the real estate and related ETF markets different from the others?

Unrealistic assumptions, multiple layers of investors and obscene prices in the commercial real estate market are all part of the reason why the current housing bust is costlier and more complicated than previous ones, comment Mara Der Hovanesian and Dean Foust for BusinessWeek. Average housing prices have already plummeted 41% from the 2007 peak.

Forecasts about the world’s demand for energy are getting dire. We’ve got a big appetite now, but it’s about to get much, much bigger. The increased pressure could be good news for energy-related ETFs.

Worldwide energy demand is forecast to rise by about 40% between now and 2030. According to the International Energy Agency, the supply of oil will need to hit 130 million barrels per day by then, up from the 85 million barrels produced per day in 2008.

On Saturday, the House of Representatives took big steps in overhauling the nation’s healthcare system. Now the pressure is on Senate Democratic leaders to follow suit, as President Barack Obama puts new pressure on Democrats in Congress to finish their work on health care before the year is up. Will related exchange traded funds [ETFs] stand to gain?

We are about two steps away from health insurance reform in America, says Obama. Stephanie Condon for CBS News reports that Democrats in the House managed late Saturday night to pass their comprehensive healthcare bill by a vote of 220 to 215. Meanwhile, 39 Democrats voted against the bill, even after adding to the legislation a strict anti-abortion measure intended to earn the support of moderates.

Earlier this year, oil ETFs were lagging oil prices by a wide margin thanks to contango. Although the situation has improved, it brings to light a situation that futures-based commodity funds can experience.

In the last month, United States Oil Fund (NYSEArca: USO) has been lagging oil prices slightly: it’s up 10.4% in the last month, compared to about 10.7% for oil prices. PowerShares DB Oil (NYSEArca: DBO) is up about 10.2% in the same time period.

Sweden is anticipating a stronger-than-expected recovery in the world economy. However, the country’s Central Bank will maintain its relaxed monetary measures, supporting the country’s fragile economy and related ETF.

Sweden’s government upgraded its economic outlook to an expected contraction of 4.9% this year, followed by 2% growth next year and unemployment estimates for 2010 were lowered to 10.7% from 11.4%, as stated in BusinessWeek.

Although not as impressive as the stock market’s gains since March 9, in the last year Bbb-rated companies have returned 38%. So the next question becomes: what do we expect those bonds and related ETFs to do next?

Investment-grade corporate bonds may have lagged the overall broad market’s gains, but from a bond standpoint, their performance has been outstanding. Jeffrey R. Kodnett for Kiplinger asks what can be expected from single-A to triple-B bonds.

Three online retailers are caught up in a pricing slugfest in an attempt to capture greater market share. No matter which company comes out on top, retail ETFs may reflect the surge in consumer spending as the price war intensifies.

Wal-Mart (NYSE: WMT), Target (NYSE: TGT) and Amazon (NasdaqGS: AMZN) are engaged in an online price war over DVDs, reports Jeremy Hobson for Maretplace.

Are you worried about that ETFs you’re holding could be gearing up to close down? Check out these signs to see if there’s cause for concern or if you’re just being paranoid.

First things first: If your ETF is going to close down, you will not lose all of your money. You also won’t wake up one day to find the fund dead and buried with no warning. Providers make an announcement of closure well before it actually happens to give investors time to act accordingly.

The United States dollar is currently so weak that people are beginning to ask if it’ll ever claw its way back. While the role of the dollar is sorted out, ETFs can help you play its present and its future.

Is the world finally losing its appetite for the U.S. dollar? Michael Schuman for Time asks the question. There are signs that we should be concerned:

The price of crude oil and its ETFs have been creeping up and there are signs that indicate the commodity could very well continue to rise.

Most recently, crude has soared north of $80/barrel and Lee Loweel of Investment U states that the price could continue to rise as hedge funds that have been sitting on the sidelines for months begin to find a home in the oil markets.

Emerging markets exchange traded funds (ETFs) have raked in about $26 billion so far this year, which has sparked concern that all this hot money is feeding a growing asset bubble. But is this so?

Some fear that this so-called “mindless money” is being thrown at these markets, distorting valuations and pumping up a potentially monstrous bubble. (Find out how bubbles form and how to avoid them). Several markets, such as Brazil and Peru, are up 100% this year.