DeliPlayer - A free audio player for Windows capable of playing AY files (and other formats such as SID, MOD and MP3).
Lieves!Tuore - Home of MYMPlay. Available for MSX, ZX Spectrum and Amstrad CPC.
Project AY - Music and software for the AY soundchip (as used in the ZX Spectrum 128K).
SND Player - A specialized musicplayer for the 16/32bit Atari computers. SND Player can, as the name suggests play ".snd" files. These are songs using the YM2149 synthesizer which is fitted to all 16/32 bit Ataris and most Atari clones.
STsndplay - A program for playing all those old Atari tunes without the need for an actual Atari to play them.