The Verge suggests the new iPad has 1 GB RAM

Though Apple is forthcoming about processor specs and display resolution, the company often fails to mention the amount of RAM inside its devices. The original iPad shipped with 256 MB of RAM and the iPad 2 with 512 MB. Sources for the Verge claim the new iPad will up the RAM again to a respectable 1 GB.

This claim is supported by iOS developer Will Strafach (@Chronic) who studied a leaked debug output file supposedly from a prototype iPad 3. He noticed that the last line in the output says "vm_page_bootstrap: 244276 free pages and 8396 wired pages". From this information, he calculated that the new iPad would have 1 GB of RAM.

Of course, this is all rumor and speculation until ifixit can get its hands on the tablet and tear it apart in fine fashion.