After trying a host of automatic tagger tools : EasyTag, Kid3, pytagger, id3v2, iTunes itself, etc etc, I've found the perfect auto-tagging tool.
Picard by MusicBrainz. And the awesomeness is that it is GPL :-)
There is MusicBrainz integration available with Amarok, iTunes, rhythmbox, banshee, etc.. but none of the tools has as awesome and simple interface as Picard! The other tools, namely, easytag, kid3, pytagger and id3v2 use the CDDB database blindly. CDDB doesn't allow queries by track name. Only album name and artist. That is an inconvenience. Also, you cannot cluster multiple mp3 files together into one and query the database. Thus, each file has to be queried manually. More inconvenience.
Picard to the rescue! It has all those niceties + the awesome (open and free to download) MusicBrainz database to back it up and a very very intuitive and simple UI!