Are there any features like Winamp's auto tag exist for iTunes?
MusicBrainz Picard works quite well, it uses the same database as iEatBrainz but is still actively developed.  It's free, and I've had great luck with it fixing tags on some 40GB of music I had laying around from my Windows days.  

The interface is somewhat arcane unfortunately.  Check out this link that will give you some other alternative ideas.

on edit:
I went back to check out the newer version of Picard (0.12 vs 0.11), and the workflow is much improved.  A lot of the annoying things from before have been automated.  If you take a few minutes to set all the preferences to your tastes using the online help as reference, this really is a great automated tagging app.