I use Taghycardia and occasionally tagscanner (both are free, for PC). Taghycardia is a highly automated tagger that greatly simplifies the task of preparing downloaded albums for putting onto my iPhone. The program prompts on any tag inconsistencies or missing crucial info (album, artist, etc.) whenever it cannot correct an error automatically. In addition, it can auto-download and embed missing album art if the corresponding option is selected. In addition, sometimes I use tagscanner for perfecting tags manually in my hdd mp3 collection.
