Sony 4GB Pro DUo Mark 2 £14.99 delivered (also 8GB £29.99)
The Memory Stick PRO Duo media from Sony gives you maximum storage for your compact digital camera, portable audio device, or PSP Handheld Entertainment System. With a huge total storage capacity of 4 gigabytes and a wide operating temperature range of -13 F to 185 Fahrenheit, It provides you with durable, high capacity storage for your digital files.
One-third the volume and half the weight of standard-size Memory Stick PRO
Delivered with a Standard adaptor
High speed data transfer
Enabling high-resolution moving image recording due to Minimum write speed guarantee
Compatible with copyright protection technology ("Magic Gate")
Just bought a 'red' W170 at amazon for £132 so this should fit this nicely.