Not all scanners are supported under Linux, make sure you buy a supported model.

Drivers

In the kernel nothing special is needed; most scanners use an USB interface and the kernel supports that (via libusb).
However, each scanner uses a special USB protocol. On Linux the package needed to make supported scanners work is SANE. This provides an API to access all supported scanners (each supported scanner must have the corresponding SANE backend installed).

Epson

For recent Epson scanners you need the Epkowa SANE backend. This backend is open-source and developed by Avasys. It comes with a graphical front end called iscan (which just accesses the SANE API). On Gentoo the package is called media-gfx/iscan.
Unfortunately, you must sometimes use binary closed components (interpreters). Those are available on the Avasys site. Gentoo is not a supported distribution though (yet) so you must extract the needed files from the RPM / Debian packages. You may have to run a special command!
Some ebuilds can be already written for such components. For instance there is an ebuild on Bugzilla for the Epson V300 Perfection.

Several choices:
- xsane
- skanlite (using libksane)
- iscan (only for Epson scanners)