QGIS Python Plugins Repository
Plugin: Vector Text Field Statistics
This plugin finds all text fields in a vector layer, identifies discrete values in each field, together with how many features have each value.
I wrote this to help with visualising OpenStreetMap osm2pgsql tables. These tend to be wide (one column per tag) and sparse (most features have null).
This has proven useful with other datasets, especially those with no metadata or documentation.