8GB Sony Memory Stick Pro Duo $149.99 @ Frys.com
Frys.com now has the 8GB Sony Memory Stick PRO Duo on sale for $149.99 plus shipping. As of the time of this post the listing says to call for availability but you might want to keep an eye on the site if you're interested in some serious storage for your PSP.
8GB Sony Memory Stick PRO Duo @ Frys.com