Originally Posted by LoganK
The 'id="cover"' trick has worked for me every time. (In fact, for books that don't have a cover at all, I drop the jpeg in there, and add a line like '<item href="cover.jpg" id="cover" media-type="image/jpeg"/>' to the manifest of the opf.)
I'm not sure what you are doing differently that would cause it to not work. Two suggestions are refresh the list (use the drop-down in the upper right to change the sort order ... someone else claimed this worked for them), and, obviously, reboot your nook color.
The jpeg thumbnail issue with Calibre will likely be addressed soon.
I was at the end of my rope lol.
I just pasted the line as you have it and changed the cover to match and that fixed it for Epubs. Any idea how to make them show up on PDF magazines?