Blimey, I didn't realize we reached 256GB already. Green House has released their latest SDXC UHS-I memory card, the GH-SDXCUA256G. Coming in 256GB of capacity, this high-speed memory card comes with MLC NAND Flash memory chips, a UHS-I rating and can deliver read and write speeds of up to 78MB/s and 50MB/s, respectively.

The GH-SDXCUA256G retails for a whopping 49,800 Yen (about $497)

Google translated:

Green House Co., Ltd. is pleased to release new SDXC card of 256GB that supports high-speed SD bus interface to "UHS-I" and "GH-SDXCUA256G". 

The "GH-SDXCUA256G", in an optimal ultra-high-speed model for high-speed fire and records HD video stable for a long time, if used in compatible devices ※ high-speed SD bus interface UHS-I, maximum read 78MB / s, maximum I can achieve high-speed transfer of writing 50MB / s. 3 year warranty with the product, portable hard case, easy to carry, INDEX seal to be able to put in hard case with memos are also supplied as standard. In addition, reduced by approximately 30% paper material as compared to the conventional package, this product adopts the eco package that completely eliminates the plastic material. This reduces the mass of the whole than the conventional package, we will contribute to the reduction of CO2 emissions in the transport, such as when compared to conventional products. 
※ In the non-UHS-I compatible devices, I realize the transfer rate speed standards as set forth by the SD Association of "Class10".