Go on caraudiosecurity.com and have a look. They're good guys to deal with too.
I got a JVC AVX KW640 from them 12 months ago, has all the bells and whistles apart from satnav and blutooth which are extra add ons, at extra price. That didn't bother me anyway as it was cheap and I can always use my tomtom.
It looks good in a mk4 but in all honesty I don't think id pay that extra difference in price to get a double din. I never ever watch DVDs; any sort of media Infact. I'd rather pay a decent premium for a good SQ single din, something like an Alpine or Pioneer.