Although Ready Boost hasn't turned out to be a great performance enhancing feature in Windows Vista, it does seem to have received support from the flash memory device manufacturers. PQI has taken a different approach and released an internal solution that fits directly onto a USB header on your motherboard. The DOM (Disk on Module) is available in four sizes, 256MB, 512MB, 1GB and 2GB with prices ranging from US$23 for the entry level model and then increasing by about US$8 for each size up to 1GB, with the 2GB unit coming in at around US$72, making it almost twice as expensive as the 1GB model.
Although this is a novel idea, it's hard to see the point of this device. It means you don't need to have an external USB key sticking out the back of your PC, but that is the only benefit it brings over a standard USB key. One interesting possibility would be if you could boot from it, as it could make for a great companion for a media center machine if you run some kind of Linux version on it, such as GeeXboX, as you don't have to waste drive space on the OS.
You can find PQI's website here