Using MusicBrainz for CD Lookup
Mediamonkey can utilize the MusicBrainz FreeDB Gateway, as an alternative to the default freedb, to lookup cd metadata.
The only setting that needs to be changed in Mediamonkey is in the Tools > Options > Network settings, enter "freedb.musicbrainz.org" for the server (without the quotes) and select HTTP for the protocol.
The beauty of using the Musicbrainz gateway is that the metadata there is generally of high quality and consistency.
If a disc does have an ID in MusicBrainz, then you can easily create a user (@ Musicbrainz) then add the discID (with PicardQT) and/or add/correct metadata fairly quickly via the freedb import or manual add release pages.
More details about MusicBrainz can be found at their own wiki.