From the GDC:
"That's crucially important in the next generation of consoles, even more so than it is today, because we have the ability to do unbelievably insane graphics on these next-gen consoles, but we still have relatively low amounts of memory. In fact, I got a video card yesterday from NVIDIA which has probably twice as much memory as the next-generation video consoles are going to have - and that's only a video card!"
http://www.gamesindustry.biz/content_page.php?aid=7189
sounds like 256 MB is going to be the standard, maybe a little more or a little less, for next-gen consoles. looks like 512 MB is out.
*CRY*