The Pledges Grid in the Fundraising Module allows you to see and filter the pledges by the due date. To see overdue pledges you can filter the Due Date column to be "Equal to or Before" and enter the date as today's date. Or you can use the filter in the side bar for Due Date. 

You can then use the Actions menu to do a Print/Email Mail Merge to send reminders. See this article for more "How can I send pledge payment reminders?"