I use iTunes primarily to sync music to my iPod, but other than that I use it to play music as opposed to streaming like Pandora or Spotify. I'm trying to completely convert from Win7 to Fedora and if I was able to have my music in a Linux environment, I'd be one step closer.
For copying stuff into your iPod, use
gtkpod, works for my iPod Shuffle at least
For streaming, and support of spotify / last.fm etc., use
On a more general note, pretty nearly anything is better than iTunes - Apple is usually excellent with user-interface design, but that program is an unusable abomination. I'd think "WTF were they thinking?" except that it's obvious that usefulness to the user was decidedly a second-class consideration compared to being a walled-garden storefront for Apple to sell music.