Some strongly typed collections in the System.Collections.Specialized namespace are StringCollection and StringDictionary, both of which contain values that are exclusively strings.

The CollectionsUtil class creates instances of case-insensitive collections.

Some collections transform. For example, the HybridDictionary class starts as a ListDictionary and becomes a Hashtable when it becomes large. The KeyedCollection is a list but it also creates a lookup dictionary when the number of elements reaches a specified threshold.

Reference

Other Resources