Sample script that lists statistics for existing Indexes, ordered by user_updates. When an index I used it is inserted into sys.dm_db_index_usage_stats. If an index is not used it will not appear in sys.dm_db_index_usage_stats. This script, contributed by Microsoft's Tom Davidson, requires SQL Server 2005.

Visual Basic
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select 
	* 
from 
	sys.dm_db_index_usage_stats 
order by 
	user_updates desc