list cast
There are many ways to do that, I think there are two you should consider:
You can use Cast and ToList, but it will require using System.Linq.
var listOfStrings = new List<string>() { "foo", "bar" };
var listOfObjects = listOfStrings.Cast<object>().ToList();
To avoid that, you can use new List<T>(IEnumerable<T> source) constructor. Because IEnumerable<T> is covariant, you can do following:
var listOfStrings = new List<string>() { "foo", "bar" };
var listOfObjects = new List<object>(listOfString);