The speed of RAM in today's graphics cards is just as important as the speed of the GPU, number of pixel pipelines and a host of other key factors in determining its performance. Advances in GPU ram have made a lot of progress in recent years, far away from the days when they all used the same memory that a CPU might.
GDD5 promises to be the next big thing for graphics cards, as it nears a potential acceptance by JEDEC as a new standard. GDD5 looks to bring significant advances over GDDR3, the most common RAM used in video cards today. In fact, Qimonda is claiming their memory will outperform existing GDDR3 by a factor of three, reaching speeds as high as 20GB/sec per module, with the ability to access multiple modules at once.
It's still a long ways off, but it is a nice preview of what we can expect for the future of video cards.