Try doing a Google search for "ddr memory pcb routing techniques". Doing that search I came across a few documents, one being this one: DDR Document from Freescale
Also, you might want to contact the DDR Manufacturer you plan to use, since most likely they probably have a set of guidelines that they can provide you.
There is an industry standard for DIMM modules which basically tells tyou how to lay out a memory module. Unfortunatly, everyone here that might tell me where to find the doc's are out. Something about a holiday???