It would be so awesome if iPod touches came with SD card slots. They're like little computers anyway. They should definitely consider adding them to the 5th generation devices.
It would be really great, but I'm convinced Apple will not put SD card slots in it. Maybe they'll create their own memory cards, so they can make them expensive, and you're forced to buy them instead of cheap SD cards.
Better get a 32GB or 64GB for 4th generation devices. With the increased resolution images, videos, apps ect. take up a lot more space.