MusicBrainz Picard for the hard work, Mp3Tag for anything not in the MB database. Both free, and once you've worked out Picard you'll never go back!
http://musicbrainz.org/doc/MusicBrainz_Picard
http://www.mp3tag.de/en/
Editor
DVD REVIEWER
MYREVIEWER.COM
My Flickr Photostream
View > File Browser
Drag and drop a folder with an album into it from the file browser column to the middle one (Unmatched files)
Click any track there, click Lookup. It should open your web browser and show a bunch of matches for that track/album, so you can find the correct release (I tend to go by number of tracks), and click the green Tagged button.
Tab back to Picard and you should see the release you clicked in the browser appear on the right column. Then just drag and drop the files in the middle to the right, if they match well (it tries on filename, existing tags and song length) it should show X/Y Z.
X is the number of songs it thinks match, Y is the number of songs in that album, Z is the number of changed files it will save. Expand the folder you should see what I mean.
Also to get cover art working you need to download the coverart plugin from the plugin page on the MusicBrainz site.
Editor
DVD REVIEWER
MYREVIEWER.COM
My Flickr Photostream