Предположим, у вас есть коллекция класса Department:
public int DepartmentId { get; set; }
public string DepartmentName { get; set; }
Затем используйте анонимный тип, подобный этому:
List<DepartMent> depList = new List<DepartMent>();
depList.Add(new DepartMent { DepartmentId = 1, DepartmentName = "Finance" });
depList.Add(new DepartMent { DepartmentId = 2, DepartmentName = "HR" });
depList.Add(new DepartMent { DepartmentId = 3, DepartmentName = "IT" });
depList.Add(new DepartMent { DepartmentId = 4, DepartmentName = "Admin" });
var result = from b in depList
select new {Id=b.DepartmentId,Damartment=b.DepartmentName,Foo="bar" };