Most of the music I download is correctly tagged due to the high
requirements put upon the source by its parent source.
I'm assuming you're downloading this from somewhere, at which point I think you almost always get funky metadata.
Otherwise, Media
Monkey has an auto-tag feature that will retrieve information and I can
choose what to apply and whether or not to write id3 v1, v2, or both.
And which do you have applied? Gilbert mentioned you could get interesting results from having both applied to a file, and you should probably consider stripping any existing tags before setting your own.
Lastly, I know nothing about MediaMonkey, but try a good metadata editor like Banshee, MusicBrainz Picard, or Cowbell. Those have been known to work well. (Personally, I favor Picard because of the vast amount of work it can do in automatically tagging your tracks and the level of quality you get from MusicBrainz.org.)