So how has 2005 been treating you?

Maybe you're ahead by a little. Maybe you're behind by a bit. The S&P 500 is off by nearly 2% through the first six months of 2005, so it's fair to say that you may very well be exactly where you were when the year began.

Then again, maybe you were lucky enough to own one of the 40 stocks trading at $5 or more that has doubled so far this year. Go back to the end of last June and you will find 194 stocks that fit the same bill of capital appreciation.

If you're like way too many investors, you probably wouldn't even bother with those stocks unless you owned them already. They have had their run. They must be overvalued. Clearly, they have already been discovered. The upside appears limited from such fresh and lofty heights.

Hogwash!

Any study of superior returns will teach you that great investments double over and over again. That's why Motley Fool co-founder David Gardner fared so well in picking the greatest growth stocks of the 1990s. He had no problem buying into companies with high relative-strength ratings.

Great stocks climb. Multi-baggers, by definition, just keep doubling. If you have ever owned an amazing stock that you wound up selling way too early, you probably know exactly what I'm talking about.

That's why I spent the Fourth of July weekend picking apart stock screens that generated some of the top performing companies over the past year. It's why I have no problem singling some out right now as candidates for continued appreciation. Sure, there is a fair deal of risk involved here. Gravity cuts both ways. But look into these stocks a little closer. I think that you, too, will like what you see:

Internet Initiative Japan (NASDAQ:IIJI) -- After watching America Online retreat in Latin America because of the onslaught of regional competitors, I'm not going out on much of a limb when I state that Internet access is something that is best handled by a local company. Yes, the world is migrating online and the need for speed is a bonus for broadband providers. Just keep the investments homegrown. Like China? Meet China Netcom (NYSE:CN). Hot for Europe? Try Deutsche Telekom (NYSE:DT) on for size. Still, if you want to bet on a pure play on Japan's Internet adoption, Internet Initiative Japan is a welcome wager.

The company has been around for a dozen years and traded publicly for the last six. It has doubled since last summer, though the stock has been on a bit of a roller coaster over the past two months. A lot of that stems from a poorly timed stock offering that was ultimately called off, but it's not something that should sell the company's potential short. This fiscal year IIJ is expecting to grow revenues by 11%, with margins improving to the point of showing a 28% spurt in profitability.

Intuitive Surgical (NASDAQ:ISRG) -- Robotic arms in the operating room? Yep. It's really happening. There are more than 300 guided arms toiling away out there given the popularity of Intuitive's da Vinci Surgical System. Thanks to new unit sales and its high-margin monopoly on accessories and maintenance, Intuitive's growth and fat profitability have been fiscal Sistine Chapels.

In the March quarter, sales rose by 54% and net profits grew tenfold. The biggest testimonial for the company's surgical-room breakthrough is that recurring revenues have gone from a third of the company's sales mix three years ago to half of total revenues today. This isn't just a more dependable source of income. It also means that hospitals, surgeons, and patients are turning to the robotic arms more often.

Gaming Partners (NASDAQ:GPIC) -- Making sure that whatever happens in Las Vegas stays in Las Vegas, Gaming Partners is using RFID technology to make sure that casino operators know where their chips may fall. Embedding RFID microchips in casino chips has many practical applications. It's not just the immediate inventory tallies that find so many companies scrambling to the RFID standard.

Gaming Partners' product also makes sure that chips don't just walk out of the casino or that counterfeit chips aren't brought in. Yes, the company is profitable. Yes, with new gaming establishments sprouting all over the place, there isn't going to be a shortage of customers anytime soon. The stock has been a five-bagger over the past year, yet it's still an obscure entity. I like that. I like that a lot.

Sirius Satellite Radio (NASDAQ:SIRI) -- Bulls may feel that Sirius can double easily because the stock is trading in the single digits. Bears may feel that Sirius is doomed to meander, at best, because it already commands an $8.7 billion market cap. At the risk of alienating both camps, I would like to point out why both cases are flawed.

Bulls? Yes, Sirius appears low-priced on a per-share basis, but you have to multiply that by the massive 1.3 billion shares outstanding to realize that the market already respects the company. Bears? Consider another satellite provider like DirecTV -- losing money and facing much more competition in the television arena than Sirius will ever have -- commanding a price tag of $21.5 billion.

The reason that I think that Sirius will eventually keep clocking in higher is that I see satellite radio continuing to surge in popularity as it expands its revenue streams. That will be great news for both Sirius and its only licensed competitor, XM Satellite Radio (NASDAQ:XMSR). It's not just the notoriously celebrated move of Howard Stern to Sirius come January. For the most part, that's already priced into the stock. It's that satellite radio is going to continue to attract the most rabid radio listening fans, and some amazing things can happen when you command a willing audience with disposable income to spare.

Turning in a pair of double plays
What do you think? Have you come across a company that may be riding a wave of favorable momentum lately? Think it can keep it going? If so, you're probably just the kind of investor who would appreciate our Rule Breakers newsletter service. In fact, one of these four stocks is an active recommendation. A subscription will land you thick in the hunt for the next batch of ultimate growth stocks.

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The year 2005 is still young. Who knows? The next double may very well be the next stock you buy.

Some other ways to double your pleasure and double your fun until I return next week with four more stocks that appear poised to double again:

Longtime Fool contributor Rick Munarriz thinks that nothing is cooler than the unassisted triple play. He does own shares in Intuitive Surgical. The Fool has a disclosure policy. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.