Do you mean metadata and album art? I just edit metadata without any program (right click file -> Properties -> Summery), it's simple. For Album art I use iTunes the, free with an account and high resolution (600x600). The only problem is iTunes stores the album art locally and does not attach it to the file itself. So I have to play the file, copy the album art shown on the left, paste the art on my desktop, copy again, and then edit the metadata through iTunes with one last copy/paste to save the image to the file.
Most of the current media players will do this for you, but it screws up the information sometimes. I always edit the files myself now, since iTunes thought my MGMT CD was disturbed and my Chili Peppers CD was a compilation (it wasn't).
