ddr

Ive been wondering why I dont hear much about DDR2 memory. Its been out for some time now, and yet most of the RAM I see on the internet is still DDR1. With DDR3 scheduled for release in 2007, why is its predecessors predecessor still the norm?

what is the best ddr mb ram to buy, i nead to make my 256mb to 516mb(dont know exacly). so what is the best one? i know about the kingson ones but is there a better one, and it must not be ti expensive.