I'm proposing to add soundtrackcollector.com to Other Databases Whitelist. Soundtrackcollector.com is valuable resource for anything related to soundtrack genre. Database has discography pages for 9942 composers including almost 50000 titles (=release groups). Almost 36000 releases have front cover pictures.

Editors at MusicBrainz actively link to this site on their edit notes. Soundtrackcollector.com url can be found from over 12000 edit notes!

Examples:

Release Group:
http://musicbrainz.org/release-group/455f56d1-5258-36c2-ba84-921a6fa4fcda
has entry
http://soundtrackcollector.com/title/5751/Jurassic+Park

Artist:
http://musicbrainz.org/artist/53b106e7-0cc6-42cc-ac95-ed8d30a3a98e
has entry
http://soundtrackcollector.com/composer/9/John+Williams

Description page at http://musicbrainz.org/doc/Other_Databases_Relationship_Type/Whitelist could include "Title pages should be related to MusicBrainz Release Groups".