var str = '[font *****] ****]*[ [/font]';
    var re = /\[[^\[]+?\]/gi;
    str = str.replace(re,'');
    alert(str)

------解决方案--------------------
\[[^\]]*?\].*?\[[^\]]*?\]

------解决方案--------------------
C# code
string str = @"[font *****] ****]*[ [/font]";
        Regex re = new Regex(@"(?is)\[font\s+[^]]+\](.*?)[[^[]/font]");
        foreach (Match ma in re.Matches(str))
        {
            Response.Write(ma.Groups[1].Value);
        }
        /*
         输出
        ****]*[ 
        */