One of the most readily available (if still relatively rare) video synthesizers is the simple but effective Atari Video Music. It has appeared in many music videos and on many blogs. It is poplar with VJs, synthesists and hifi buffs.
It is however as far as I know only available in NTSC not PAL and only rarely do they turn up in Europe. Even if one did you would need a converter. Of course the UK has its own vintage music visualizer the
Chromasope.
However both of these are expensive and hard to find. Help is at hand if your in the mood for some DIY with The Pixelmusic 3000 designed and built by Tarikh Korula based on the Parallax Propeller and detailed in Make issue 14! The code is for NTSC but I think it can be altered for PAL. Also see
gadgetgangster for a kit based of the Pixelmusic project.
I may give it a go!