Bit Tech has a guide to learn you how to add more storage capacity to the Asus Eee PC. They take a 32GB Flash Voyager USB stick from Corsair and show you how they integrated it into the Asus Eee PC.
The Eee PC has three external USB ports, which is more than enough for something of this size. This particular mod solders into a pre-existing USB port rather than trying to create a new one. This will of course leave you with only two external ports, but this is still an ample amount and can always be added to with a USB hub.
Corsair has been kind enough to provide us with a massive 32GB Flash Voyager. At around £175, this is getting close to the cost of the Eee PC, but still offers pretty good value for all that space. The 16GB version comes in at around £75, which is a little easier to swallow, metaphorically speaking. Physically, they are both the same dimensions – so either will work. Although you could use other brands of flash drive, there is no guarantee that they will fit inside the Eee PC, as this is all we have tested with.