The world of exchange traded funds (ETFs) provides so many choices and sometimes, finding a particular sector ETF becomes daunting. But this short list should help narrow it down for you.

Specialty-sector ETFs, or “thematic” ETFs, have become a hit with investors, covering more than 40 unique themes in the market with more than $10 billion in assets under management, according to IndexUniverse.

While some consider thematic ETFs “gimmicky” and believe these forms of ETFs are only popular when the media is hyping the sector, they have their advantages and an investor should be aware that such options are available.

Specialty ETFs can help round out a portfolio and allow investors to take advantage of different segments of the market. To spot opportunities, watch the trend lines.

Alternative energy. Skyrocketing energy prices have brought more investor interest to all sorts of energy investments. The largest alternative energy ETF is PowerShares WilderHill Clean Energy Portfolio (NYSE Arca: PBW), currently up 23.4% year-to-date, with $743 million in assets under management. PBW is more focused on U.S.-listed companies.

Coal. The cheapest energy source of BTUs. Ever-increasing oil prices are encouraging the development of the coal. The largest coal ETF is Market Vectors Coal ETF (NYSE Arca: KOL), currently up 1.3.4% with $277 million in assets. KOL primarily includes mid-cap miners, weighted 49% in U.S. companies, 23% in China and 15% in Indonesia.

Nuclear. Once operational, nuclear power is seen as the cheapest kind of energy, but the industry is still grappling with the issue of nuclear waste. The largest nuclear ETF is Market Vectors Nuclear Energy ETF (NYSE Arca: NLR),  currently up 21.7% year-to-date, with $166 million in assets. NLR has a 40% allocation to uranium miners, with other weightings in power generation and plant construction firms.

Commodities. ETFs are an easy way for a commodity trader to access this area of the market. The largest hard asset commodity ETF is Market Vectors Agribusiness ETF (NYSEArca: MOO), currently up 40% year-to-date, with $1.5 billion in assets. Other areas include water resources, steel, timber and broad-based commodities.

Infrastructure. Infrastructure covers companies involved in construction and repair of roads and bridges, building and maintaining power grids, telecommunication networks and sewage systems. Worldwide stimulus funds have been steadily injecting more money into the sector. The largest infrastructure ETF is iShares S&P Global Infrastructure Index Fund (NYSE Arca: IGF), currently up 12.9% year-to-date, with $267 million in assets.

Transportation. There’s no denying the economic impact of transport systems. The Claymore/Delta Global Shipping ETF (NYSE Arca: SEA) is currently up 25.9% year-to-date, with more than $70 million in assets. SEA is a good indicator for economic activity and commodities demand.

Green. The green sector provides environmentally-friendly technology for an evolving society. The largest green ETF is PowerShares Cleantech Portfolio (NYSE Arca: PZD), currently up 29.8% year-to-date, with $145 million in assets. PZD tracks the performance of companies whose products improve productivity while reducing consumption of natural resources.

Other. Or “miscellaneous” category that includes gaming, luxury items and Chinese real estate to name a few. The largest ETF in this area would have to be Market Vectors Gaming ETF (NYSE Arca: BJK), currently up 46.7% year-to-date, with $108 million in assets. BJK tracks global gaming companies.

Max Chen contributed to this article.

Tags: Agribusiness, Alternative Energy, BJK, Coal, Commodity ETFs, Energy, Gaming, Green ETFs, IGF, Infrastructure, KOL, MOO, NLR, Nuclear Energy, PBW, PZD, SEA, Sector ETFs, Shipping, Transportation