Occasionally someone asks me for my advice on software for a specific job such as image editing, or in this case, managing their digital music collection. While this question hasn't come up recently it has in the past so I thought I would share my answer here. I have used winamp, microsoft's media player, itunes, foobar2000, and a few other's before finally settling on MediaMonkey - it is a fantastically feature rich tool that does almost everything I want it to - and what it can't do out of the box I can add thanks to the fact that it supports user created scripts/tools/plugins.
MediaMonkey adds all the features I wish winamp had (my previous favorite tool) while also supporting all of the plugins that are written for winamp. Additionally, MediaMonkey makes it easy to update the information about all of your songs, to create playlists, find music, create CDs, convert CDs a to digital format, organize your music on your computer, download album art, synch to your mp3 player/phone, and a bunch of other stuff - it's almost ridiculous how much this thing can do.
However, if you have a ton of music and you need to get a lot of album art there isn't a quick and easy way built in. Fortunately, thanks to the user script feature, someone has created a great tool to query Google and to get missing album art. - it's the script titled "Batch Art Finder" and it works very well.
While there are some problems with MediaMonkey they are typically pretty trivial and don't do anything to tarnish my overall excellent impression of the package. I can't recommend it highly enough. You can get a nearly feature complete version of MediaMonkey for free (same with winamp) however I liked MediaMonkey so much I paid for the "Gold Version" which gives me some additional search and playlist creation tools. Give it a try and let me know if you like it.