Using QGIS is nice, and provides a solid interface for interacting with the DBF, but if you need to do something programmatically or just want tools to inspect shapefiles, I thought I'd mention a few other tools: I often use the basic features of shapelib for examining DBF files: it can add, create and modify both geometries and attributes, I often use
dbfdump myshape.dbf to get a quick overview of the attribute values.
Another option if you're interested in programmatic control of a DBF is dbfpy, a python library (an an alternative to the nice
foreign library mdsummer mentions). An example script for adding a column:
db = dbf.Dbf("myshape.dbf", new=False)
# add a new character field named 'myfield'
db.addField(("myfield", "C", 15))