Best Buy: Best Sales Yet to Come  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  nation's top electronics retail chain, posted a 21 percent rise  in quarterly profit on Wednesday, slightly above expectations,  and said the holiday shopping season was even more competitive  than last year.