Archaeologists have clustered objects, assemblages and inscriptions found at archaeological excavations, to date them and explain their cultural origins.
Demographers have clustered parish register records, to deduce the social and genetic consequences of ancestral migratory patterns.
Economists have clustered regional wage rates, to identify areas of homogeneous wage profiles across a range of occupational groups, and thereby estimate wage premia by authority type.
Educational Psychologists have clustered students, to model academic attainment and improvement for different student groupings.
Geographers have clustered farm census districts, to map the distribution of different agricultural activities and measure changes in productivity. Mapping example here.
Legislators have clustered the treaties of the European Parliament, to derive operational classifications of current EU laws.
Librarians have clustered publications by keywords and citations, to produce efficient subject groupings for title indexation, abstraction, updating and retrieval.
Linguists have clustered language and speech varieties, to trace their evolution and develop a taxonomy of semantics.
Political Scientists have clustered voting results, to reveal voting factions and thereby forecast future ballot results.