Many GIS offer the ability to view the attribute table of a vector layer. While this is perhaps less obvious in the R environment, it is not impossible. The following command allows you to visually inspect, and change any data.frame (or other vector, matrix, etc.), including Spatial*DataFrames.
invisible allows you to close the viewer without filling the
console with the attributes of the table. You could also use:
new_data = edit(spatial_layer@data)
to assign changes made to the data to a new variable, or use:
spatial_layer@data = edit(spatial_layer@data)
to make changes to the Spatial*DataFrame itself.