Please download the attached file for the queries and explanations of how the results should be used. Included are:
1. Find "Missing" Indexes for the entire instance of SQL Server
2. Find "Missing" Indexes for a single table
3. Examine the current index structure for a single table
4. Look at index usage for a single table
5. Look for possible bad indexes inside the entire current database
6. Drill into your workload (Bonus)
(source: Glen Berry's SQL Server Performance blog)