This deal has ended.
Buy.com has the 1gb Sandisk Memory Stick Pro Duo for only $29.95 after a $12 mail-in rebate valid through 7/23. Any memory stick can be used in any Sony device, from PSPs to digital cameras to TVs. The non-Sony ones are usually most affordable, as in this case. Shipping is free and there is no sales tax (except to CA, MA, MD, TN).