This Nifty Minidrive product will get you about 64GB of extra storage space, depending on which microSD card you put in it. Fits entirely within the built-in SD card reader slot.

I currently have a number of these elago Nano II compact USB microSDHC card readers . Amazingly compact, the only real limitation is they do not yet fully support microSDXC cards. Up to 32GB with SDHC cards, they work quite nicely.