All of these will give you an IEnumerable<string>
:
You can use an explicit constructor to build and populate your collection:
new List<String>( ddlTransportadora.Items.Select( x => x.Value ) )
You can use LINQ to create an enumerable collection on the fly:
ddlTransportadora.Items.Select( x => x.Value ).ToList()
ddlTransportadora.Items.Select( x => x.Value ).ToArray()
You can even skip creating an actual collection and simply use LINQ deferred execution to provide an enumerable view of your data:
ddlTransportadora.Items.Select( x => x.Value )
Why try to make things any more complicated than they need to be?