From the "Sold Database": USA Canada Australia Roy
One of many APS Stamp Store covers...
and one from Canada...
While I do not go out of my way to collect them, I do enjoy finding Americana series stamps on cover. I think this is my highest dollar-denominated "cover". Postage due dollars.
This one totals out at $47.70 (but may have been overfranked a bit based on the manuscript): Not really a cover, but you can get just about anything cancelled at a first day ceremony! This is my favorite. A cover franked to include insurance to deliver QI1 - a Parcel Post Insurance booklet. Sweet!
Forgot this one - without die cut no less: