[what is the best nVIDIA graphix card out in shops and how much is it?

That would probably be the GeForce 7900GTX. Its just out so you
will have to pay alot to get one of them. I took a quick look and
the price tag here seems to be € 599,-

Although personally I would go for this card:

Asus Extreme N7800GT DUAL



It reminds me of the good old VooDoo 5 6000 This card is actually a SLI setup
on one board. Price tag however is not so nice: € 769,-

wow very posh if i must say so myself