Android: Whether or not you use Winamp on a Windows system and enable wireless syncing, there's a few things to recommend Winamp for Android. It's got a good, better-than-default interface, it supports Shoutcast streaming stations, and can import iTunes libraries and playlists. In other words, it makes you think about using Winamp on your desktop.
That's not to say that Winamp in its 1.0 release isn't in need of some tender care — commenters at the Android Market do note some problems with ID3 tags and a need for an EQ function. But given how handy a Winamp desktop/Android combination can be, it's an upgrade any Android user bored with the standard Music app should consider.
Winamp is a free download for Android systems, and requires its desktop counterpart to provide wireless syncing.