Export Artwork is a well known and appreciated tool to export cover art from iTunes and import them from Amazon. The program lets you specify parameters like whether setting album cover for one track or a whole album. All you have to do is select the tracks in iTunes that you want to process and Export Artwork will work automatically. You can set 3 different image formats (jpeg, png or tiff) and although slightly limited, Export Artwork gives you a choice of four name formats to choose from.
Similarly the export features are pretty advanced. You can limit the size of album covers that you want to fetch and choose to import artwork for all albums or only those that have no cover. Export Artwork will automatically embed the artwork to the track's ID3 tag. Quick and highly flexible, Export Artwork is an essential tool for any serious iTunes library owner.