Mp3tag is the manual way, you'll have to add all the data yourself.
Oh wait I'm an idiot, you're right, I forgot Mp3tag also has a search function for MusicBrainz, Discog, etc. built in. I've been using it for so long but only to manually correct tags.If the files are already ripped, it can export the file name to the tag or vice versa.
Mp3Tag is what you're after. It's free and is really powerful - particularly at batch renaming in bulk.