I used to think iTunes was the best media player (for both Windows and my Mac). It had a clean interface, low resource requirements and (with the help of a couple of add-ons talked to the media keys on my Vaio and kept my Last.FM account up-to-date and scrobbled)
Then along came release 6 and the rot set in. Release 7 is bloated, slow and no fun any more. I know 7.01 fixes a lot of that (and I'm sure they're hard at work) but that, and things like the fact that new iPod functions like the fast selection won't be available as firmware upgrades to older players, has pretty much soured me on the iPod (anyway, I've found a better use for it now and I use my K-Jam to listen to music)
Around the time I was losing faith in iTunes WMP11 went into Beta and became a firm favourite. Worked with my media keys, supported Last.FM plug-in and even the Windows Live Writer "Currently Listening" functions, low system, overhead and it looked darn good.
But it didn't support .m4a audio tracks properly (I know there are some tag reading plug-ins, and it does import the tracks into an "other" part of the library). Music is music. Leaving aside the DRM issues I don't care if it's Ogg, m4a, mp3, WMA or whatever the next greatest thing is going to be (I hear Vinyl is making a resurgence these days!). And of course it can't keep my iPod up to sync (I know I said it wasn't important, but I still have some music on the old half-brick)
Enter my new friend SongBird. It's fairly lightweight. It runs on WinXP, OSX and various Linux flavours. It's based on the Mozilla foundation products (you know, that other browser... firefox). It includes support for Audioscrobbling to Last.FM and a whole bunch of other extensions (Wikipedia artist lookup, Shoutcast streaming audio directories etc). It supports my media keys and is very agnostic about audio formats (happily playing .m4a as well as other formats, and even imports my iTunes playlists). It even has an extension to allow me to sync my iPod should the mood ever take me.
It doesn't support the "Currently Playing" add-on for Windows Live Writer yet though :(
Update:the Currently Playing support rocks ;)
The only real downside for most people is that SongBird is very much a fledgling product. As I write it's at it's 0.2 developer preview release and it wasn't people that it may explode. It's not exploded for me yet but your mileage may vary. At the very least I hope the iTunes and WMP teams take a look at it and see what they can do in the war to win the hearts and minds of their users...