As explained in another thread here (German), I currently use external command-line tools with Mp3tag to generate Replay Gain values. (By using Mp3tag’s »export« feature to generate a batch file that in turn calls the appropriate command-line tools. I then invoke the batch file via an icon on the Quick Launch Bar.)
Tychos’s metamp3 (v0.92 beta 5), metaflac, and vorbisgain.
So for me it’s all back to just two tagging utilities: Mp3tag and MusicBrainz’ Picard for the MusicBrainz-related stuff. And yes, I’m happy that I can do Replay Gain »in Mp3tag«, so to say.