This is a nice query using sys.dm_db_missing_index_details, sys.dm_db_missing_index_group_stats and sys.dm_db_missing_index_groups to find out which indexes is missing.
SELECT CAST(SERVERPROPERTY('ServerName') AS [nvarchar](256)) AS [SQLServer],
db.[database_id] AS [DatabaseID],
db.[name] AS [DatabaseName],
id.[object_id] AS [ObjectID],
id.[statement] AS [FullyQualifiedObjectName],
id.[equality_columns] AS [EqualityColumns],
id.[inequality_columns] AS [InEqualityColumns],
id.[included_columns] AS [IncludedColumns],
gs.[unique_compiles] AS [UniqueCompiles],
gs.[user_seeks] AS [UserSeeks],
gs.[user_scans] AS [UserScans],
gs.[last_user_seek] AS [LastUserSeekTime],
gs.[last_user_scan] AS [LastUserScanTime],
gs.[avg_total_user_cost] AS [AvgTotalUserCost],
gs.[avg_user_impact] AS [AvgUserImpact],
gs.[system_seeks] AS [SystemSeeks],
gs.[system_scans] AS [SystemScans],
gs.[last_system_seek] AS [LastSystemSeekTime],
gs.[last_system_scan] AS [LastSystemScanTime],
gs.[avg_total_system_cost] AS [AvgTotalSystemCost],
gs.[avg_system_impact] AS [AvgSystemImpact],
gs.[user_seeks] * gs.[avg_total_user_cost] * (gs.[avg_user_impact] * 0.01) AS [IndexAdvantage],
'CREATE INDEX [Missing_IXNC_' + OBJECT_NAME(id.[object_id], db.[database_id]) + '_'
+ REPLACE(REPLACE(REPLACE(ISNULL(id.[equality_columns], ''), ', ', '_'), '[', ''), ']', '')
+ CASE
WHEN id.[equality_columns] IS NOT NULL
AND id.[inequality_columns] IS NOT NULL
THEN '_'
ELSE ''
END + REPLACE(REPLACE(REPLACE(ISNULL(id.[inequality_columns], ''), ', ', '_'), '[', ''), ']', '') + '_'
+ LEFT(CAST(NEWID() AS [nvarchar](64)), 5) + ']' + ' ON ' + id.[statement] + ' (' + ISNULL(id.[equality_columns], '')
+ CASE
WHEN id.[equality_columns] IS NOT NULL
AND id.[inequality_columns] IS NOT NULL
THEN ','
ELSE ''
END + ISNULL(id.[inequality_columns], '') + ')' + ISNULL(' INCLUDE (' + id.[included_columns] + ')', '') AS [ProposedIndex],
CAST(CURRENT_TIMESTAMP AS [smalldatetime]) AS [CollectionDate]
FROM [sys].[dm_db_missing_index_group_stats] gs WITH (NOLOCK)
INNER JOIN [sys].[dm_db_missing_index_groups] ig WITH (NOLOCK)
ON gs.[group_handle] = ig.[index_group_handle]
INNER JOIN [sys].[dm_db_missing_index_details] id WITH (NOLOCK)
ON ig.[index_handle] = id.[index_handle]
INNER JOIN [sys].[databases] db WITH (NOLOCK)
ON db.[database_id] = id.[database_id]
WHERE id.[database_id] > 4 -- Remove this to see for entire instance
ORDER BY [IndexAdvantage] DESC
OPTION (RECOMPILE);