As the second quarter draws to a close, the S&P 500 (^GSPC -0.88%) hasn't seen a better first-half return since 1998, with the index having risen nearly 13% through Friday's close. A loss of 1.5% in June was the index's first monthly decline all year, but it still managed to remain above the 1,600 even under pressure from uncertainty about the next move for the Federal Reserve and its ongoing efforts to stimulate further economic growth.

But a few of the stocks in the S&P 500 have performed particularly well this year, and some of those names might of the Dow's stocks have done even better than the overall average. Let's look at the three stocks in the S&P that have managed to double in price during the first six months of the year and see whether further gains are in the cards for the companies.

Best Buy (BBY 0.20%), up 133.9%
Arguably the most interesting thing about Best Buy's huge gains in 2013 is that most investors remain immensely skeptical about the stock. In particular, naysayers have largely ignored any potential profits from the partnerships that the big-box retailer has managed to score with major technology companies such as Microsoft and Samsung to open store-within-store concepts. Yet even if the mini-stores themselves don't drive sales, they might increase overall customer traffic to Best Buy, and that could reverse the troubling trend that has led the company to consider smaller stores in attempts to cut overhead.

The challenge Best Buy will face is that many of its rivals in the mobile space are looking at similar business models going forward. The advantage Best Buy will have over carrier-owned store chains is in carrying multiple carriers under one roof, but that might not be enough to complete a successful turnaround.

Netflix (NFLX -9.09%), up 128%
The story for Netflix this year has been content, as the company has made deals with outside content providers as well as coming up with its own original content. In arenas ranging from children's programming to hit series, Netflix has held its own even against some much larger competitors in the space.

Netflix is right to pursue deals as quickly as possible in the hopes of building up a strong enough network effect to hold off potential new competition. The strategy has no guarantee of success, but in combination with its aggressive international growth plans, Netflix could well keep rising and regain levels from before the streaming/DVD split if it can meet its own expectations for growth.

Micron Technology (MU -4.61%), up 126%
Micron might seem like an unlikely candidate for this list, given its somewhat pedestrian status as a memory-chip maker. But the cyclical industry has definitely been on a major upswing lately, as demand for memory for solid-state drives and mobile devices has given Micron new sources of potential revenue.

Still, the company is waiting on closing on its long-awaited deal with Japan's Elpida Memory, which will vault Micron into the upper echelon of DRAM memory producers and give it valuable customer contacts to boost its memory sales for use in popular mobile devices. Only once that deal is complete will we see just how much growth it can produce for Micron going forward.

What's next for the S&P?
Investors can only hope for second-half results that are as strong as what the market delivered during the first half. While the lightning-fast pace of such huge gains clearly isn't sustainable over the long run, these three stocks have the potential for further share-price appreciation if their businesses can keep delivering the improvement that has helped boost their popularity so far in 2013.