There are a heap of them on the winamp plugins site http://classic.winamp.com/plugins
I can't remember which ones I use, and I'm currently on the other side of the country to my car
The one I normally use is actually a fade-into rather than a cross fader. It mixes the tracks perfectly for live albums, so I get a smooth transition into the next track, rather than an annoying break. For random play, it means the tracks start immediately too, instead of being faded over for a couple of seconds as would happen with a cross fader.