StringBuilder

 Class
    public static string CustCenter()
    {
        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        sb.AppendLine("<img src=\"\" alt=\"센터\" style=\"margin-bottom:10px\" />");
        sb.AppendLine("<img src=\"\" alt=\"글쓰기\" />");
        sb.AppendLine("<ul>");
        sb.AppendLine("<li><img src=\"\" alt=\"글관리\" /></li>");
        sb.AppendLine("<li><img src=\"\" alt=\"스킨\" /></li>");
        sb.AppendLine("<li><img src=\"\" alt=\"플러그인\" /></li>");
        sb.AppendLine("<li><img src=\"\" alt=\"링크\" /></li>");
        sb.AppendLine("<li><img src=\"\" alt=\"환경설정\" /></li>");
        sb.AppendLine("</ul>");

        return sb.ToString();
    }

.aspx.cs
custCenter.InnerHtml = CommonClass.CustCenter();


.aspx
<div class="custCenter" id="custCenter" runat="server"></div>