Don't settle for anything but USB or Firewire scanners (NO paralell port or serial based ones, they are slow!).
Try to get the highest color precision as well... Such as 42 or 48-bit color. 32-bit and 36-bit color scanners look washed out to me.
The more expensive it is, the faster and better it usually is, so keep in mind you get what you pay for (usually..).
Check to make sure what you are getting is Windows XP compatible as well. Not all scanner brands are XP compatible.