You can always use winamp to find your missing tags. To do so,
1- Right-click on a file or selection
2 - Send to:
3 - Auto-Tag
Winamp will connect to Gracenote Media Database to search for the missing tags of your files. It does not always work but it's pretty effective compared to other methods, specially when you have lots of unsorted files like me!
You could try using the Musicbrainz.org tagger to identify your audio files. It uses a unique audio fingerprinting technology to generate a fingerprint of the audio and matches it against a huge user contributed database to identify your file, even if it is not tagged properly.