After using mediamonkey for a long time, lately I have felt that it langs behind in many areas. It's funny how an app that formerly dominated the category can lose control and slip down...
Anyway. For just playing, I posted about
XMplay, and I still think this is the best choice.
But for organizing libraries (and mainly get accurate cover art), MM used to be the best (google art plugin, amazon, etc). It was buggy, and doing it in batches was a pain; I can remember how much time I invested getting cover art in a half-automatic way when I first found MM...
Enter
mp3Toys. Just play with it. it makes everything so automatic and smooth, it's ridiculous. But it's probably the opposite of XMplay: sound quality is not the focus, and with a large library it may take > 100Mb of memory.
Impressive integration with last.fm (it recommends similar artists!), very accurate cover and lyrics finding... I'll let you find more.