I've been looking at these for a while, but am still waiting for prices on a reasonable size (9-10"+) to come down. The bigger/more expensive ones appear to have internal memory and can download from a CF/SD/etc. card or a USB drive. The smaller/less expensive ones seem to require the storage media to be plugged in all the time.

Since they all seem to show pix in 800x600 or so, and with random 32-96MB cards laying around from long ago, I imagine I could load up a large number of down-sampled images on spare media without a problem. If not, 256MB cards can be bought for $20 new, 128MB cards are on ebay for $8 including shipping.