I used mp3Tag editor to modify tag data for some of my mp3's. I was having trouble with Sync on my Ford recognizing some of the songs and it was because I was missing some tag data. mp3Tag is free and very easy to use. I was able to load >6000 mp3's and view tag data. This was handy as I could scroll through the data to see what was missing. It did take awhile to load that many songs as you might expect.
I even found out by looking at the data that I had some .wma files mixed in with my mp3's so I deleted them. They can be deleted from the program.
I found mp3Tag very useful and easy to use.