Ok so all of you have your opinions on what music player is your favourite, and here is mine.
We all know of the standalone software that Microsoft bundles with Windows and we all know of the horrid that iTunes is, but many of you probably don't know of something called foobar2000. Foobar is the best music player out there, mainly for one reason: Customisability.
When you install foobar (it's also only a mere 3MB when installed), you start off with something that does not look too flash hot. But if you do some searching on the Interwebz, you will find a plethora of "components" (or addons in Layman's terms) that can do so much to make your music experience as awesome as possible. Things like an iTunes-esque layout (I use it and love it), popups that display what song is being played (again, love it too!), lyrics, automatic taggers, ratings, autoscrobblers (for all you Last.fm users!) and many skins that alter the appearance, if you can think of it, it's most likely around somewhere!
Then we get to the built-in stuff. Foobar can be configured to look at any folder on your system to update the internal music library. If any music is added or removed to / from your music folder, foobar automatically detects the change and updates the list to display, so adding more music is a LOT easier! Add in keyboard shortcuts that are fully programmable (there are a LOT of options here, I doubt anyone would need ALL of them!), gapless playback, full ASIO support (for all you audiophile out there), ability to rip audio CD's in pretty much ANY audio format... The list continues for ages!
Above is a poll for what you lot use to playback music, will be interesting to see what you use!