Here is the code we are using for the purpose of cloning Opportunity line items: 

<apex:page standardcontroller="OpportunityLineItem" extensions="cloneOppPrd_Extension" tabstyle="OpportunityLineItem">
<!-- Provide fields so that we don't need to query them within the apex class -->
<apex:outputpanel rendered="false">
    {!OpportunityLineItem.Launch_Date__c}
    {!OpportunityLineItem.OpportunityId}
    {!OpportunityLineItem.Volume_Tier_List_Price__c}
    {!OpportunityLineItem.UnitPrice}
    {!OpportunityLineItem.Service_Type__c}
    {!OpportunityLineItem.Quantity}
    {!OpportunityLineItem.PricebookEntry.ProductCode}
    {!OpportunityLineItem.PricebookEntry.Name}
    {!OpportunityLineItem.PPM_Price_Per_Thousand__c}
    {!OpportunityLineItem.ListPrice}
    {!OpportunityLineItem.Launch_Date__c}
    {!OpportunityLineItem.Geotargeted__c}
    {!OpportunityLineItem.Fixed_Price__c}
    {!OpportunityLineItem.End_Date__c}
    {!OpportunityLineItem.Expected_Performance__c}
    {!OpportunityLineItem.Description__c}
    {!OpportunityLineItem.Custom_Quote__c}
    {!OpportunityLineItem.Brand__c}
</apex:outputpanel>
<!-- Custom clone button and form, allows users to clone and make modifications during the clone process -->

<apex:form >
<apex:sectionHeader title="Clone Opportunity Product" subtitle="Clone of {!cloneopp.PricebookEntry.Name}"/>
<apex:pageblock >
    <apex:pageBlockButtons >
        <apex:commandbutton action="{!Save}" value="Save"/>
        <apex:commandbutton action="{!Cancel}" value="Cancel"/>     
    </apex:pageBlockButtons>
    <apex:pageBlockSection columns="2" title="Product Information">
        <apex:outputField value="{!cloneopp.OpportunityId}"/>
        <apex:outputField value="{!cloneopp.PricebookEntry.Name}"/>
        <apex:inputField value="{!cloneopp.Fixed_Price__c}"/>
        <apex:inputField value="{!cloneopp.Service_Type__c}"/>
        <apex:outputField value="{!cloneopp.PricebookEntry.ProductCode}"/>
        <apex:inputField value="{!cloneopp.Custom_Quote__c}"/>                                      
    </apex:pageBlockSection>

    <apex:pageBlockSection columns="2" title="Order Details">
        <apex:inputField value="{!cloneopp.Launch_Date__c}"/>
        <apex:inputField value="{!cloneopp.Brand__c}"/>
        <apex:inputField value="{!cloneopp.End_Date__c}"/>
        <apex:inputField value="{!cloneopp.Geotargeted__c}"/>
        <apex:inputField value="{!cloneopp.Description__c}"/>
        <apex:inputField value="{!cloneopp.UnitPrice}"/>        
        <apex:inputField value="{!cloneopp.ListPrice}"/>
        <apex:inputField value="{!cloneopp.Quantity}"/>
        <apex:inputField value="{!cloneopp.Volume_Tier_List_Price__c}"/>
        <apex:inputField value="{!cloneopp.PPM_Price_Per_Thousand__c}"/>                                                                                            
    </apex:pageBlockSection>
    
    <apex:pageBlockSection columns="2" title="Forecasting">
        <apex:inputField value="{!cloneopp.Expected_Performance__c}"/>
    </apex:pageBlockSection>
    

</apex:pageblock>
</apex:form>
</apex:page>

GeorgeB11, this looks great!  Thank you very much.

Will you please also post the class body of the cloneOppPrd_Extension apex class?

Much thanks!

CaleAtSpecificMedia

public with sharing class cloneOppPrd_Extension {

    private final OpportunityLineItem oli; 
         
    public cloneOppPrd_Extension(ApexPages.StandardController stdController) {
        this.oli = (OpportunityLineItem)stdController.getRecord();
    }
    
    public OpportunityLineItem cloneopp; 
    public OpportunityLineItem getCloneopp(){
      if(cloneopp == null)cloneopp = oli.clone(false,true);      
      return cloneopp;        
    }

  public Pagereference save(){
    insert cloneopp;
    Apexpages.Pagereference retURL = new PageReference('/'+cloneopp.id);
    retURL.setRedirect(true);
    return retURL;
  }      
    
    static testmethod void testOppPrdClone(){
      
    Account a = new Account(Name = 'Test Account');  
    insert a;        
    Opportunity opp = new Opportunity(name='test opp', stagename='New', CloseDate=System.today(), AccountId=a.id, Commission_Information__c = 'Media Only');          
    insert opp;  
    Product2 prod = new Product2(name = 'test product', External_ID__c = 'testxid');
    insert prod;  
    Pricebook2 pb2 = [select id from Pricebook2 where IsStandard =: true];    
    PricebookEntry pbe = new PricebookEntry(UnitPrice=1, Product2Id=prod.id, Pricebook2Id = pb2.id,IsActive=true);
    insert pbe;        
    OpportunityLineItem oppLine = new OpportunityLineItem(UnitPrice=1,Quantity=100,description__c='test',expected_performance__c=80,PricebookEntryId=pbe.id,OpportunityId=opp.id,Launch_Date__c=system.today(),End_Date__c=system.today().addDays(365));      
    insert oppLine;
            
      ApexPages.StandardController sc = new ApexPages.StandardController(oppLine);      
        cloneOppPrd_Extension controller = new cloneOppPrd_Extension(sc);    
      
      PageReference pageRef = Page.cloneOppPrd;
        Test.setCurrentPage(pageRef);              
        
    controller.getCloneopp();
    controller.save();
  
      
    }
    
}

Holy stuff!!! This is great!

Eleventy billion internets awarded to you good sir!

CaleAtSpecificMedia