SD cards aren't the only way to "Expand" memory... There's a ram pack available.. eeproms are easily added... And you need to make friends with Mr Google... He (or She) is the person that can find your answers... fastest and easier than any other means..
Your questions might be a great deal more on point if you do your own basic research first...
Obviously your ram requirements are unknown at this time since you failed to mention the use for the extra memory or how much you require... or whether the "memory" needs to be fast
So here is a solution... Assuming that ram fits your idea of memory, Here is a link to 512 KB of ram.. http://ruggedcircuits.com/html/quadram.html
there are various cards that supply SD card slots .. I have a dozen or more, both on other shields or stand alone.
There are various shields that can supply EEprom storage as well, both populated with some kind of EEprom or you can buy and install what you require...