Sony Memory Stick Micro M2, 16GB, only £17.99!
Memory Stick perfect for the PSP Go! to increase your capacity!
The 'M2' media is approximately one-quarter the volume of 'Memory Stick PRO Duo' media, yet only about 1.2mm thick. 'M2' media is designed as an externally removable media with a controlled eject function to prevent users losing the media.
On the same website the 8GB version is £19.99, so £2 less for twice the capacity.
Cheapest I could find it new elsewhere was £35 odd.