I've always found EasyTAG (easytag.sf.net), to be a great program. If you have your files named correctly, you can use EasyTAG to create tags automatically, based on file names and folders. So if you had a folder named "John Williams" and inside that a folder named "Star Wars Episode I" and inside that all your tracks, named something like "01 - Title.flac" you could have EasyTAG automatically tag your files with artist, album, tracknumber and title, just based on the file hierarchy and name.

Not sure what OS you're using, but EasyTAG is available for both Windows and Linux, or if you're on Mac OS X, there's a Fink port, although those are often pretty rough to set up, if you're only trying to get one program.