You have to implement a TypeConverter for your class and override the GetStandardValues and GetStandardValuesSupported method. In your override of GetStandardValuesSupported you have to return true. In your override of GetStandardValues you should return the list of values.
Optionally you can override GetStandardValuesExclusive and allow the user to specify values that are not in the value list.
Note: The standard values collection can be initialized at runtime depending on the context of the instance object.