<apex:dataTable value="{!acc}"   var="a" cellpadding="4" border="1" rows="3">
            <apex:column headervalue="account name"  width="20">
                 <apex:inputField value="{!a.Name}"/>
            </apex:column>

             <apex:column headervalue="account site" width="20" >
                    <apex:inputField value="{!a.site}"/>
              </apex:column>

              <apex:column headervalue="account phone" width="20" >
                    <apex:inputField value="{!a.phone}"/>
              </apex:column>
    </apex:dataTable>
 </apex:pageBlockSection>

 <apex:pageBlockButtons location="BOTTOM">
    <apex:commandButton action="{!insertNewItem}" value="save"/>
</apex:pageBlockButtons>

insert acc;

    acc= new list<account>();
  for(integer i=0 ; i<3 ;i++){
     account ac = new account();
     acc.add(ac);}
  return null;