We would like to see which records have an attachment attached from the list view.  To do this, we created a checkbox field HasAttachment, default unchecked, and the following trigger.  If the Expense custom object record has an attachment, then the HasAttachment field should update to TRUE.  We tested this trigger through 'Upload File' under the Notes and Attachments related list, however, the HasAttachment field remains unchecked.
 

trigger AttachmentonExpense on Attachment (after insert) 
{
Set setParentId = new Set();
List Expenselst = new List();

for(Attachment att: Trigger.new)
{
setParentId.add(att.ParentId);
}

Expenselst = [select Id , HasAttachment__c from Expense__c where Id IN :setParentId];

For(Expense__c e : Expenselst)
{
e.HasAttachment__c = True;
}

update Expenselst;
}