Source: http://stackoverflow.com/questions/616718/how-do-i-get-common-file-type-icons-in-c

    public static class FileIcon
    {
        [DllImport("shell32.dll")]
        private static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);

        [StructLayout(LayoutKind.Sequential)]
        private struct SHFILEINFO
        {
            public IntPtr hIcon;
            public IntPtr iIcon;
            public uint dwAttributes;

            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public string szDisplayName;

            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
            public string szTypeName;
        };

        private const uint SHGFI_ICON = 0x100;
        private const uint SHGFI_LARGEICON = 0x0; // 'Large icon
        private const uint SHGFI_SMALLICON = 0x1; // 'Small icon

        public static System.Drawing.Icon GetLargeIcon(string file)
        {
            var shinfo = new SHFILEINFO();
            var hImgLarge = SHGetFileInfo(file, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), FileIcon.SHGFI_ICON | FileIcon.SHGFI_LARGEICON);
            return System.Drawing.Icon.FromHandle(shinfo.hIcon);
        }

        public static System.Drawing.Icon GetSmallIcon(string file)
        {
            var shinfo = new SHFILEINFO();
            var hImgLarge = SHGetFileInfo(file, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), FileIcon.SHGFI_ICON | FileIcon.SHGFI_SMALLICON);
            return System.Drawing.Icon.FromHandle(shinfo.hIcon);
        }
    }