Winamp is a solid choice, and it still has some features I wish Windows Media Player had. Namely that there's an "add" button to add files to your playlist. With WMP you have to open the folder and drag it in if you want to add it. Opening the file clears whatever is already there. Plus it has lots of coll kins. I've used MMD3 skin forever...because it looks really nice and is functional.
With that said, WMP has always had the advantage of being able to be minimized and retain playback controls in the taskbar, which I love. I used to not use it because version 10 was a dog...rather slow to load up. I'm running version 12 on Windows 7 and just like everything else on 7, it's very fast loading. Plus it has better support for finding and downloading music within the player, with Winamp you have to use the web browser. I also find it's ripping and burning controls to be easier to use. Even when I used Winamp almost exclusively for playing music, I would use WMP for burning. The other advantage WMP has is that it's video playback is a lot better. Half the time when I try to play a video in Winamp, the video window doesn't automatically pop up,which is annoying. So I use WMP for that too.
There other media players out there, but those are the two I use the most.
I haven't used Real Player in forever, and I quit using iTunes a long time ago. I really hate how when Apple wants to update iTunes it wants you to install a whole new program (Safari) too.