Check out the Canon CanoScan N1220U. Scans are as good as the Epson Perfection 1200U (albeit slower), but it's so slim and lightweight, you could carry it around like a book or file. Furthermore, it doesn't need a power supply, it draws power directly from the USB cable.
BTW The Perfection 1200U is excellent too. I am using the scanner, BTW. However, I just got to review the Canon scanner this month... if I hadn't got my Epson then, I would have gotten the Canon instead.
atwl