The idea of paying for merchandise with a smartphone isn’t exactly new. The technology to make it work has been in use since 2010, starting primarily with Google (Nasdaq: GOOG) Wallet.

By the end of 2011, Visa (NYSE: V), Apple (Nasdaq: AAPL) and a consortium called Isis — which included telecom names Verizon (NYSE: VZ) and AT&T (NYSE: T) — were all offering some sort of mobile payment service. None of them have gotten a great deal of traction though, partially because consumers may be overwhelmed by too many choices and partially because few retailers are equipped to handle this type of payment.

Times change, however, and with smartphones or other handheld devices set to take a decisive lead as the way with which consumers interact with the rest of the world, the mobile payment business should hit a needed, self-sustaining critical mass in 2013. It’s very likely Isis will fall by the wayside, yielding to more prolific services from Google and Apple. But, it’s still quite possible the mobile payment market can support more than one service provider. After all, retailers have been accepting cash, checks and credit for decades. Adding a couple of ways to take digital payments is certainly no leap now.

It’s hardly new, but diabetes is a growing problem. And just to be clear, it’s not growing simply because the world’s population is growing.

As our diets collectively worsen, the percentage of people developing diabetes is actually increasing; 2013 may well be the tipping point from “serious” to “epidemic.” It’s estimated that 8.3% of the U.S. population had diabetes in 2011, according to the American Diabetes Association.

So, in much the same way cancer vaccines were all the rage in 2010 and hepatitis C spurred some acquisitions early in 2012, it’s time for diabetes to take the spotlight for a while.

A few weeks worth of strong growth data can be chalked up to chance. The rate of growth in new construction has spanned far longer than a few weeks, however.

In October, the annualized start rate of 603,000 single-family homes was the highest pace we’ve seen since 2008 when they were on the way down, according to a report by the U.S. Department of Housing and the U.S. Census Bureau. The same goes for issued permits. Multi-family housing starts and permits are also well into the strongest levels we’ve seen since 2009’s lull, and all starts and permits data have been persistently on the rise since February 2011. It may not be red-hot growth, but slow-and-steady counts for something.

Though the uber-cheap natural gas prices we were all enjoying in late 2011 and early 2012 have finally been unwound, it’s still cheap at around $3.55/MMBtu. In fact, this price level may be the ideal balance between “affordable for consumers” and “profitable for explorers.”

As long as it can hold up around that price, cost-effective explorers and drillers like Ultra Petroleum (NYSE: UPL) can turn a profit, but won’t have to worry about less efficient competition sneaking into the game. And as it stands right now, natural gas appears to be getting comfortable in the $3-4 range. There’s one ancillary beneficiary to the deep plunge in natural gas prices last year — natural gas vehicles (NGVs). Though NGVs are not new, fleet managers looking for a way to cut costs made a massive number of conversions to compressed natural gas powered vehicles.

Although natural gas prices have ramped up a little since then, it’s still cheaper to use cheap natural gas (CNG) than gasoline to power these fleets. Look for more retrofits and conversions in 2013, which is great news for stocks such as Westport Innovations (Nasdaq: WPRT) and Clean Energy Fuels (Nasdaq: CLNE). Both serve the natural gas vehicle market.

Though the world’s capacity to manufacture solar panels is still about twice the actual need, not every alternative energy technology is long on promise and short on actual results. The trick for investors will be finding the renewable energy technologies that are within reach of profitability (as an industry), and more attractive than fossil fuel sources of energy.

This criterion largely excludes wind, solar and biomass. It doesn’t exclude geothermal and hydroelectric, however. Both are sources with the know-how and infrastructure already in place, and each offers low-hanging fruit for energy providers. Think about U.S. Geothermal (NYSE: HTM) and Ormat Technologies (NYSE: ORA) as ways to invest in this sector.