Do you use the PO / Requisition Listing report? This is a great way to get a list of all "On Order" Purchase Orders, all open orders from a certain year, or orders by PO Type.
To run the report, open the Purchase Orders module from Acquisitions. Use the Reports menu to launch "PO / Requisition Listing."
You can use any of the fields that are helpful to you, but especially take a look at PO Type, PO Status, and Reporting Period.
A final tip: if you do not fill in any dates, this is a great report to run on a recurring basis. For example, you could set up the report to send you an email on the first day of each month with all "On Order" POs.
To do this, set the Output Parameters to your email, Run as Batch Job, and set the Frequency. (Bear in mind, however, that if you set any dates in the listing criteria, those will stay the same every time a recurring Batch Job runs.)