Here are some rules for you snort freaks to chew on that I have found useful in web heavy environments.

alert tcp $HTTP_SERVERS $HTTP_PORTS -> any any (msg:"ET ATTACK RESPONSE x2300 phpshell detected"; content:"Locus7Shell"; nocase; classtype:web-application-activity; reference:url,www.rfxn.com; sid:300010; rev:1;)
alert tcp $HTTP_SERVERS $HTTP_PORTS -> any any (msg:"ET ATTACK RESPONSE RFI Scanner detected"; content:"RFI Scanner"; classtype:web-application-activity; reference:url,www.rfxn.com; sid:300020; rev:2;)
alert tcp $HTTP_SERVERS $HTTP_PORTS -> any any (msg:"ET ATTACK RESPONSE lila.jpg phpshell detected"; content:"CMD PHP"; classtype:web-application-activity; reference:url,www.rfxn.com; sid:300030; rev:2;)
alert tcp $HTTP_SERVERS $HTTP_PORTS -> any any (msg:"ET ATTACK RESPONSE ALBANIA id.php detected"; content:"UNITED ALBANIANS aka ALBOSS PARADISE"; classtype:web-application-activity; reference:url,www.rfxn.com; sid:300040; rev:2;)

alert tcp More >