Educate yourself on business card scanner software
Choosing a document scanner is largely dependent upon many factors, not the least of which is image resolution. If you plan to use your document scanner mainly for filing text or less sensitive graphic documents, you can make do with a document scanner that has a resolution of 600 dpi or less. For most uses that don't require too much detail, this resolution is generally more than enough. For more demanding applications however, you may want to look into a higher resolution document scanner. If you are planning to scan photographs as well as documents, you may want to look into a flatbed document scanner.