A fairly powerful freeware tool I regularly use is Mp3tag and also supports various other codecs such as Ogg, WMA, FLAC, MPEG4, etc. This tool supports ID3 version 1 & 2 tags, embedded cover art, multiple sub directories and importing from freedb and text listings (e.g. the song title list from an online shop). I mainly use it to insert the tag information based on the file names or vice versa.
Their website and download link can be accessed here.