Do you mean a new external screen to be connected via the mini-DVI port?
Everymac.com states that "Apple reports that this model supports "digital resolutions up to 1920x1200" and "analog resolutions up to 2048x1536”.
A mini-DVI to VGA adapter would be necessary for the “analog” resolution.
Looks like just about any low/mid priced monitor will suffice as long as you have the proper connectors, digital or analog.