Circuit City Posts Weak Sales; Shares Off  NEW YORK (Reuters) - Circuit City Stores Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=CC.N target=/stocks/quickinfo/fullquote"&gt;CC.N&lt;/A&gt;, the  No. 2 U.S. electronics chain, on Monday reported a surprise 4.3  percent drop in quarterly sales at stores open at least a year,  signaling a further widening gap with top rival 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;.