I personally use a 4GB Memory Stick, and I find it's ridiculously huge. It's much more storage than I could possibly ever need ... and that's a good feeling. Sure, there's an 8GB stick coming down the line, but you certainly won't get such a sweet deal for quite some time. FRYS.com has a 4GB SanDisk card for only $70, after mail-in rebate. Yes, the website lists the card as $120, but once you add it to your cart, you will see the price magically change.
[Thanks, Dane! Via slickdeals]