Supposedly specifically designed for the PSP using some kind of shiny technology they created to be better than other ones.
They cost a little more at most places but I guess it should be worth it when streaming from the MS and I aint no poorper so I couldn't care less about the price. I got it for £89.95 including delivery from [Register or Login to view links].
Some good news and bad news, I see that Sparco.com has Sandisk 1GB memory stick pro duos on sell for $95.65 plus S/H. Pretty decent price I thought. One bad note though, it says they are currently out of stock. So, if they will fully process your order, you may have to wait a little longer to actually receive one.