There was a Winamp 3 alpha release for Linux. I tried it, it was very unstable (crashed frequently), but when it did work it, it was just like the Windows version. I wouldn't bother with it.
For music players, I like Rhythmbox. It is similar to iTunes. And for video, Totem is nice.
Though Winamp 5 is currently my favorite media player. I think its safe to say there is no Winamp 5 for Linux, and probably never will be. There's no OS X version either, and no plans to create one. Hopefully someone will clone all the features in one of the free Linux players (if it hasn't been done already). It would not be too hard to clone the features I like. Is there a media library plug-in for XMMS? Tossing a media library on XMMS might bring it up to par with Winamp 5, if it worked as nicely as Winamp 5's does.