I've been using Winamp for years, since v2, the crappy v3 and the improved v5.

A lot of people seem to like Foobar2000 but when I checked it, it really lacked features that I liked in Winamp.  Happened to check it out again recently and I must say, I'm more impressed.

Mainly, Winamp 5.551 (think that's the version) seems to be a little dodgy on me - it sometimes crashes when I put the machine into sleep, and seems to take a little while to load my ~6000 songs playlist.
Foobar2000 doesn't seem to have these issues.  Also since it's a simpler interface, it uses less memory :P
Issues about it though:
- doesn't have Winamp's nice plugin interface
- can't really select sound output option (stuck with waveout?)
- interface does take a while to get used to and tweak
- I don't really use it, but it probably doesn't have as good visualisations and internet radio capabilities

One of the things I liked about Winamp was the ability to set the output to waveout and then use its global hotkeys to change the system's volume.  Although foobar2000 allows you to set global keys to do stuff like this, it doesn't affect the system volume.  For this, I happened to find Sound Control which does this.

So well, for a lightweight song player which you keep minimized most of the time, foobar2000 isn't too bad a choice.