As a Winamp user since 1998, today I replaced it with Songbird. Winamp has all the features I need (basically FLAC support and last.fm scrobbling :)), but it lacks an important feature I need in the near future: MacOS support.
Today I briefly looked at some Winamp alternatives (thanks Guido!). Some lacked the multi-platform feature, others were just plain hideous (ok, I’m not going to make friends with this statement, but players in this category always had a Linux background…).
After testing some players, I think I will settle for Songbird. The user interface is nice, the development is active, the plugin-system means that it is extensible, and it works on both Windows and MacOS (I don’t really care for Linux support for the moment; on my HTPC box that runs Linux I use XBMC for audio playback). Some features I haven’t used, but look interesting are the Android player and the transcoding when a MP3 player is synced (currently I use FLAC on my Sansa Clip which is a bit overkill).