Florian asked me to post this...
Exact Audio Copy (exactaudiocopy.de) supports GD3 (getdigitaldata.com) as a tag data source. GD3 is a subscription service, but has vastly superior and accurate disc information and album art.
It would be great if mp3tag also supported GD3. (btw, you can get a cheap lifetime subscription to GD3 for something like US$8 via EAC)
Thanks much!
./s4z