Well
DDR consists of PC2100 (266mhz) PC2700 (333mhz) and PC3200 (400mhz)
PC3200 is the general standard for last gen DDR platforms There are a few varients higher than PC3200 such as PC4000 however they are really just meant for overclocking and unless overclocked run at 400mhz.
DDR2 is the currant industry standard and comes in all sorts of flavors such as 533mhz, 667mhz and the now standard speed of 800mhz all the way up to 1300mhz. However the fastest that can be seen by most motherboards without overclocking is 1066mhz.
Now with the release of DDR3 capable boards standard DDR is 3 generations behind.