If you don't mind paying for the software, TuneUp uses Gracenote.
If you're looking for free software that uses audio fingerprinting to find information, try MusicBrainz Picard. It doesn't use Gracenote (it has it's own database) but works in a similar way.
Tune Up will automatically fix all of your tags, but I don't know how well it does with the genres. Going song by song would probably work the best. iTunes, and I'm sure a lot of other programs, will let you modify tags on multiple tracks at once. A lot of people seem to like Winamp, but I've never really used it so I don't know if it would work for what you're wanting to do.
Suggestion:
Rip the CD into MP3s, add them to your favourite music player and get something like TuneUp (http://www.tuneupmedia.com/index.php) to identify the songs through Acousting fingerprinting.
I grew up using Winamp as my default player. I was really disappointed when AOL bought them out because it never felt the same. The active community changed. I wish there was a Mac version though because I would use that. I used to use the Napster plugin for Winamp and it was awesome. I loved that player.
In iTunes, you can tell it to show duplicates. This tells you how.
I have a plugin for iTunes called TuneUp that will automatically find missing album covers and can rename unnamed tracks and albums for you. It also helps discover new music that is similar to what you're listening to. I think I actually discovered it in a Reddit sponsored ad or something.
Pre-09,before I made the switch to Android, there was this awesome software that would manage your iTunes library for you. Worked awesome. I'll see if I can find it.
Edit: here it is http://www.tuneupmedia.com
Apple is bringing the show duplicates feature back. http://9to5mac.com/2012/12/04/itunes-11-will-soon-get-the-duplicate-song-detection-that-its-predecessors-had-but-dont-count-on-cover-flow/ Also, has anyone else heard the rumor that Apple is buying TuneUp Media? http:/www.tuneupmedia.com
I used a program called TuneUp. Its not free but they offered a trial which would let you process a certain amount of tracks that would clean up and stuf. I really like the program and I found it worked really well. Oh and heres a link http://www.tuneupmedia.com/
I use Tune-up You have to pay for it but it organizes all of your motherfuckin files, deletes broken ass tracks, tells you which songs you need to complete a goddamn album, and informs you when any of the stupid musicians in your library are playing in your dumpy town. Its awesome!
You can nuke your album art folder and let iTunes start over. Make sure iTunes is off when you do this. It's located in Music/iTunes/Album_Artwork
I use TuneUp and was so pleased with it - I actually purchased it and have used it on my iTunes library of over 20K music files. They've done pretty good work maintaining it through changes in iTunes.
I've also seen this product in a box on the shelf at apple stores, Sam's Club, and BestBuy (I think, IIRC).
And they have a demo so you can kick the tires before buying it.
If you're feeling generous, they gave me a link with a referral code that gives you 15% off and me $10. But don't use it if you don't want to, the link above is a direct - no referral code - link.
Edit: rearranged text so as not to seem pushing with referral code. :)
Are you asking about organizing within iTunes, or organizing tags in songs?
Are you trying to organize music purchased directly from iTunes, or music you obtained elsewhere? (In rare occurrences, iTunes purchased music is poorly tagged)
If you are looking to do this for one album, read this:
Select a song from one of the pairings, and right click -> get info. Select a song from the other group, and right ciick -> get info. Compare the information from the two groups and see where the discrepancy is. Otherwise just copy and paste the information about the album from one to the other, and see if they then merge. (There may be a white space character somewhere preventing the merge).
This should merge them for free.
If you are looking to perform this for lots of entries, read below:
If you are trying to get the tags to match up like they would within iTunes, you will want to use the Gracenote database - which is the same database iTunes references.
I'm guessing what you are looking for is a program like this: http://www.tuneupmedia.com/
It isn't free, but it matches all your music up to the exact same database as iTunes (it uses the Gracenote database, which isn't free to access).
Alternatively, iTunes Match may do the same thing if all your music is already offered on the iTunes store. I just can't remember though if iTunes Match actually alters the tags associated with your files.
Just use this.
Dump your songs into it, get a coffee, watch a movie, and come back to a job well done.
The only slight downside is that their genre groups have a little bit more specificity to them compared to using just "rock" for everything. This app actually gives songs their appropriate genre automagically.
I have used this, http://www.tuneupmedia.com/index.php?gclid=CJuH9Oml16cCFYx_5QodoVGz9g, with great success. I apologize; I'm not a master of the reddit comment links.
EDIT: Oh crap, I just realized that in the ~3 years since I used the program, they have changed their business model. It used to be totally free. Now it's 100 songs for free, and a tiered payment system. That's dumb, but I do know the thing works.