Just thought I'd mention to anyone looking for a media manager J. River Media Center transfers the album art just fine. By the way, all my album art is stored as "folder.jpg" in the album folder, none of my album art is stored in the tag (I find this practice to be a waste of space).
Also, Media Center has a pretty good album art search tool if your music doesn't have cover art yet.
I like Media Center, but it has some issues and is kinda buggy... also it's $40. If you're thinking about using it make sure to get the demo first.