Best Buy Quarterly Profit Jumps 21 Pct.  NEW YORK (Reuters) - Best Buy Co. Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=BBY.N target=/stocks/quickinfo/fullquote"&gt;BBY.N&lt;/A&gt;, the top  U.S. electronics retail chain, on Wednesday posted a 21 percent  rise in quarterly profit and said it gained market share in the  period.