I got me one of the 1GB SanDisk special gaming MS DUO PRO's
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 http://www.digimem.biz/.
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.