$str=preg_replace("/<s*imgs+[^>]*?srcs*=s*(''|")(.*?)\1[^>]*?/?s*>/i","", $str); //过滤img标签

$str=preg_replace("/s+/","", $str); //过滤多余回车

$str=preg_replace("/<[ ]+/si","<",$str); //过滤<__("<"号后面带空格)

$str=preg_replace("/<!--.*?-->/si","",$str); //注释

$str=preg_replace("/<(!.*?)>/si","",$str); //过滤DOCTYPE

$str=preg_replace("/<(/?html.*?)>/si","",$str); //过滤html标签

$str=preg_replace("/<(/?head.*?)>/si","",$str); //过滤head标签

$str=preg_replace("/<(/?meta.*?)>/si","",$str); //过滤meta标签

$str=preg_replace("/<(/?body.*?)>/si","",$str); //过滤body标签

$str=preg_replace("/<(/?link.*?)>/si","",$str); //过滤link标签

$str=preg_replace("/<(/?form.*?)>/si","",$str); //过滤form标签

$str=preg_replace("/cookie/si","COOKIE",$str); //过滤COOKIE标签

$str=preg_replace("/<(applet.*?)>(.*?)<(/applet.*?)>/si","",$str); //过滤applet标签

$str=preg_replace("/<(/?applet.*?)>/si","",$str); //过滤applet标签

$str=preg_replace("/<(style.*?)>(.*?)<(/style.*?)>/si","",$str); //过滤style标签

$str=preg_replace("/<(/?style.*?)>/si","",$str); //过滤style标签

$str=preg_replace("/<(title.*?)>(.*?)<(/title.*?)>/si","",$str); //过滤title标签

$str=preg_replace("/<(/?title.*?)>/si","",$str); //过滤title标签

$str=preg_replace("/<(object.*?)>(.*?)<(/object.*?)>/si","",$str); //过滤object标签

$str=preg_replace("/<(/?objec.*?)>/si","",$str); //过滤object标签

$str=preg_replace("/<(noframes.*?)>(.*?)<(/noframes.*?)>/si","",$str); //过滤noframes标签

$str=preg_replace("/<(/?noframes.*?)>/si","",$str); //过滤noframes标签

$str=preg_replace("/<(i?frame.*?)>(.*?)<(/i?frame.*?)>/si","",$str); //过滤frame标签

$str=preg_replace("/<(/?i?frame.*?)>/si","",$str); //过滤frame标签

$str=preg_replace("/<(script.*?)>(.*?)<(/script.*?)>/si","",$str); //过滤script标签

$str=preg_replace("/<(/?script.*?)>/si","",$str); //过滤script标签

$str=preg_replace("/javascript/si","Javascript",$str); //过滤script标签

$str=preg_replace("/vbscript/si","Vbscript",$str); //过滤script标签

$str=preg_replace("/on([a-z]+)s*=/si","On\1=",$str); //过滤script标签

$str=preg_replace("/&#/si","&＃",$str); //过滤script标签

更简单些的写法：

function delhtml($str){  //清除html标签
$st=-1; //开始
$et=-1; //结束
$stmp=array();
$stmp[]=" ";
$len=strlen($str);
for($i=0;$i<$len;$i++){
  $ss=substr($str,$i,1);
  if(ord($ss)==60){ //ord("<")==60
  $st=$i;
  }
  if(ord($ss)==62){ //ord(">")==62
  $et=$i;
  if($st!=-1){
   $stmp[]=substr($str,$st,$et-$st+1);
  }
  }
}
$str=str_replace($stmp,"",$str);
return $str;
}

function clear_html_label($html) 
{ 
$search = array ("''<script[^>]*?>.*?</script>''si", "''<[/!]*?[^<>]*?>''si", "''([rn])[s]+''", "''&(quot|#34);''i", "''&(amp|#38);''i", "''&(lt|#60);''i", "''&(gt|#62);''i", "''&(nbsp|#160);''i", "''&(iexcl|#161);''i", "''&(cent|#162);''i", "''&(pound|#163);''i", "''&(copy|#169);''i", "''&#(d+);''e"); 
$replace = array ("", "", "1", """, "&", "<", ">", " ", chr(161), chr(162), chr(163), chr(169), "chr(1)");
return preg_replace($search, $replace, $html); 
}