var items = myDictionary.Values.ToList();
//Use Linq if you want to flattern your lists
var items = myDictionary.SelectMany (d => d.Value).ToList();
Dictionary<string, string> dicNumber = new Dictionary<string, string>();
List<string> listNumber = new List<string>();
dicNumber.Add("1", "First");
dicNumber.Add("2", "Second");
dicNumber.Add("3", "Third");
listNumber = dicNumber.Select(kvp => kvp.Key).ToList();
// Or:
listNumber = dicNumber.Keys.ToList();