Picard is great, supports Windows and Mac (probably Linux too) and many file types including flac.

The part I love about Picard is it groups tracks into albums so they should then come up with the same metadata. It uses the MusicBrainz database which is community edited. They have strict style and moderation so tracks and artists are named correctly.

I use a few addons to tweak the defaults (I'm not at my computer but would be happy to list).