You'd definitely want a scanner that utilizes CCD technology, such as the very cost-effective Epson V500 or 4490 Photo scanners for around $150-200, but no document feeder. CCD most authentically reads color information and can scan depth, both of which the inferior, cheaper CIS technology cannot do.
But one with a document feeder, my initial searches come up with a Fujitsu ScanSnap S1500 ($499) or an Epson GT-2500 Plus ($639 @ newegg).
The only advantages to CIS scanning technology (which, unfortunately, is utilized in most scanners & combo units these days) is that the units are both quicker to warm up and the size are thinner.
Sidenote: Finding a combo (printer/scanner) unit with CCD is much more difficult and expensive. I haven't found a good one that meets my reqs.
Vote your purchase dollars to CCD technology, to get manufacturers to give us more options than allowing the market to be overtaken by crappy CIS scan technology!