just cannot get my album art to show up on my iphone 4s

I've had iphones for several years so I'm not new to this but I'm stuck. I've had the iphone 3, 4 and 4s. Will be getting the 5 soon but the album/cover art is getting on my nerves.

Recently some of my album art disappeared. When I have connected to itunes it shows in the Library but even if I sync/turn off/on/delete and re-enter it shows in the Library but not the iphone.

I decided to delete all of my Library (and sync, thereby removing all of my music) to start afresh.

So, trying one album and ensuring the album art is embedded using mp3tag, winamp and tag&rename - I am absolutely sure the album art is there.

I load it into my Library and the art shows up in itunes.

I then sync that one album with my iphone. The album appears on the phone but no album art?!?!?!

I've tried and tried and tried until I'm fed up.

I've noticed that there are quite a few threads around the internet with people having problems with album art.

Is there a simple thing I am missing or doing wrong???

Thanks for any help