The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.By David Sterman NEW YORK ( StreetAuthority) -- Regular readers of my articles know that I spend most of my time in search of undervalued mid-sized and large companies. There are so many bargains in the S&P 500 alone, that it simply hasn't paid to spend too much time on small -- and risky -- stocks in recent quarters. Yet every portfolio needs a broad cross-section of holdings if it is to beat the market. This means you should hold a basket of micro-cap and small-cap stocks alongside your blue-chip holdings. To mitigate the risk that these small companies stumble badly, it pays to get a vote of confidence that business is solid. These smaller companies, all trading below $4, have all seen such a vote of confidence in the form of notable levels of insider buying.