I've got a 64GB SDXC card in mine and it works fine.
I don't believe there is any limit as long as the card is formatted to FAT32. By default, anything above 32GB will be pre-formatted to exFAT which won't work. If you're using Windows you will need to use a 3rd party utility to do the reformat because you can't format anything media over 32GB to FAT32 using the native Windows formatting tools.
I posted some instructions in the past on exactly what to do to get it to work so I'll try and find the post then put a link to it in this thread.