When you're in the market for some stocks for your portfolio, it's easy to focus on ultra-popular stocks. They're likely to be ones you hear and read about the most, after all. And many of them have been great performers -- which is why they've become popular.But you might want to be cautious with certain popular stocks, for various reasons -- such as their financial health, competitive strength, or valuation. Here are five companies to dig into more deeply before committing any of your hard-earned dollars. ...