This is always an issue for me, but over the past 4 years its been narrowed down to a choice of 3; Foobar2000, Winamp, and WMP.
WMP looks too bulky to me, and not only does the default view demand that every artist have a bloody album image, it seems to crash when you have over 60GB of music!
Winamp is probably the best at easily listing the music you want to listen to, but the skins on it suck ass, and I'm not sure if anyone else has noticed this, but if you change the settings to not have a popup for every time a new song comes on and then boot it up again, the popups still persist which is bloody annoying in certain fullscreen games - seems to eat fps :S
Foobar2000 - possibly the most customisable media player you'll find for free, but you have to download the right version - recently they've taken away the ability to slap on certain modifications and skins to it, but I hear that it can utilize the glass effect of Vista in its skins easily. Only problem is choosing your music - you have to either open another window to scroll through your music or simply drag through every song you have by every artist in alphabetical order!
So I was wondering - what media players do you guys have, and you got any suggestion as to what media player I should try?