I’ve posted before about using OpenOffice’s Calc spreadsheet for use as a DBF editor (and why it doesn’t have the serious problem Excel 2003 has with editing DBF files). But Calc isn’t really designed to be a DBF file editor per se, which means that if, for example, you want to add new data columns to your shapefile’s DBF file, you’ll need to know a bit about column data formatting, and that’s kind of a pain. For basic DBF file editing, I find DBF Explorer easier to use, since it’s designed specifically and exclusively to work with DBF files. Adding and defining data column types is easy using the “Structure” button, as is modifying the values of individual data elements and searching for specific text elements (hint: use the Tab key to move to the data record you want to change). You can also delete full individual records, but that can easily screw up the relationship between the shape data and the associated DBF records, and should be done with care. Also be aware that the DBF file is updated continuously as you modify records, so if you want to keep the original unchanged, you should edit a copy of the original file.
Not a particularly fancy interface:
but it doesn’t need to be. And the help file tells you everything you need to know.
Addendum (1/29/08): Dave McGraw points out that if you use the “Structure” button to modify some of the parameters of an existing field, like the name, it will wipe out the data in that field, which is a bad thing; it will give you a warning first, though, that you may lose some data after such a modification. Other parameters, like field type and width, seem to be modifiable without nuking the original data; adding or deleting a field does not seem to cause any problems, either. Another argument in favor of editing a copy of the original, rather than the original itself.
The author also has some other free utilities on his site, including FTP/Web/Mail server software, and a simple install file builder.