For my standard 29 inch Eagles pennants, I simply hang the mylar pennant sleeves on the wall with the 3m interlocking adhesive hangers.
For oversized pennants, I have done 2 things.
First, I had my nicest Carlisle Indians pennant framed in a large square frame, held in place with invisible stitching. Pretty expensive framing job.
For my lesser Carlisle pennants, I chose a much less expensive option, although not nearly has good from an archival standpoint. I had them shrinkwrapped on triangular pieces of board. This allows me to hang them, and protect them somewhat, and if I recall only costed around $15-$20 each. My framer also does shrinkwrapping.
