Graphics-chip vendors, and the companies that supply graphics memory, have recently discovered bin sorting. Now, everyone is getting into the act. There's Nvidia, with the TNT2 and TNT2 Ultra. Matrox is about to ship the G400 and G400Max. Then there's memory.
Some chips run the memory at the same speed as the graphics chip.
A good example of this is Voodoo3's synchronous memory interface. Other chips, such as the TNT2, have an asynchronous memory interface, allowing memory and core clock speeds to be independent of the other. The plethora of board makers for TNT2 chips have also added their own brands of user choice Nvidia guarantees the TNT2 Ultra to run at a 150MHz core clock with a 183MHz memory clock - but that's at zero airflow in a small case. Naturally, with a cooling fan and more space around the card, it will run faster. Some card vendors have taken advantage of this and are either shipping at a higher clock rate or supplying tools to let users make their own clock-rate changes.