Well I am not sure it's completely effecient in terms of coding practice but I was able to work out a solution that got rid of the SOQL in the For Loop and I was also able to concatonate all the users from the custom object with the CreatedBy user for the task.  If there are things I can do below to make this better, let me know.  As of now this code seems to be working just fine.

To fix what I had, I first changed the SOQL to capture both Informed_User__c and  Informed_User__r.Email... I then created a String named emailAddr.  I then looped through the results of the SOQL query and added the email value to that string with each pass of the loop.  (This removed the SOQL from the loop... much better for getting rid of excessive queries and potential DML limits.

Finally I added the result of the CreatedBy query to the emailAddr string by adding the following after the loop was completed:  emailAddr.Add(taskCreatedByUser);

Updated code below.

trigger SendEmailonTaskUpdate on Task (after update) {       
   	
   	//********************************************************************************
   	//	Capture the task ID from the URL for use in the emailList query
   	//********************************************************************************
   	
   	String taskId = ApexPages.currentPage().getParameters().get('Id'); 
		
	//********************************************************************************
	//  Create a list object with the informed users and append
	//		the created by user to the list for the "To" addresses
        //********************************************************************************
    List<Task_Informed_Users__c> emailList = New List<Task_Informed_Users__c>();
     emailList =  [Select Informed_User__c, Informed_User__r.Email from Task_Informed_Users__c where Task_ID__c =: taskId];
    
	String taskCreatedByUser = [select Email from User where Id = :trigger.old[0].CreatedById].Email;
	
	
	//********************************************************************************
	//	Iterate through list to create a "To" string that can be
	//		placed on one line
	//********************************************************************************
	String[] emailAddr = new String[]{};
	
	for (Integer i = 0; i < emailList.size(); i++) {
		//System.debug(emailList[i].Informed_User__c);		
		emailAddr.add(emailList[i].Informed_User__r.Email);
	}	
	
	emailAddr.Add(taskCreatedByUser);
	
    //********************************************************************************
    //	Begin constructing email message code
    //********************************************************************************
    
   	Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();     
     
    String[] toAddresses = emailAddr;
    mail.setToAddresses(toAddresses);
    
    mail.setSubject('Details : ' + trigger.new[0].Subject + ' AND ' + trigger.new[0].Status);
    
    mail.setPlainTextBody('The details for Task: ' + trigger.new[0].Subject + ' have been changed.  The Status of the task is ' + trigger.new[0].Status + '.  The Task description is ' + trigger.new[0].Description);
    //mail.setHtmlBody('The details for Task: <b>' + trigger.new[0].Subject + '</b> have been changed </b>');

    Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });

}