Album Artwork Assistant finds album cover artwork on the Internet and adds it to music track files in iTunes. Other tools like it exist, but none of them worked the way I wanted, or they cost too much.
The main feature I needed was a batch queue. When the hard disk on which I kept all my music crashed, I had to re-rip my fairly big CD collection. After the ripping, I had to add the album artwork to all tracks again. Embedding is a slow Process that blocks iTunes. That is why I wanted a tool with a queue, so I could search for a large number of CD Covers quickly and then let the program process the queue unattended while I do important Things.