I bought JR.com's Sandisk 2GB microSD Mobile Memory Kit
This thing is impressive. $25 for a 2GB micro-SD card, smaller than the proverbial fingernail. The kit includes a mini-SD and an SD adapter for the micro-SD card. The latter works in our camera, the card itself is in our BlackBerry*.
The combination of Google Checkout and J&R was likewise an excellent combination.
* I'm much less impressed with the BB, but that's another story.
Update 2/5/08: Amazon has 4GB versions for about the same price, and 2GB versions for about the price of lunch. Cue hysterical laughter, this is ridiculous.