Easiest way to Rotate a List in c#

List<T>

The simplest way (for a List<T>) is to use:

int first = list[0];
list.RemoveAt(0);
list.Add(first);

Performance is nasty though - O(n).

Array

This is basically equivalent to the List<T> version, but more manual:

int first = array[0];
Array.Copy(array, 1, array, 0, array.Length - 1);
array[array.Length - 1] = first;

LinkedList<T>

If you could use a LinkedList<T> instead, that would be much simpler:

int first = linkedList.First;
linkedList.RemoveFirst();
linkedList.AddLast(first);

This is O(1) as each operation is constant time.

Queue<T>

cadrell0's solution of using a queue is a single statement, as Dequeue removes the element and returns it:

queue.Enqueue(queue.Dequeue());

While I can't find any documentation of the performance characteristic of this, I'd expect Queue<T> to be implemented using an array and an index as the "virtual starting point" - in which case this is another O(1) solution.

Note that in all of these cases you'd want to check for the list being empty first. (You could deem that to be an error, or a no-op.)

You could implement it as a queue. Dequeue and Enqueue the same value.

**I wasn't sure about performance in converting a List to a Queue, but people upvoted my comment, so I'm posting this as an answer.

I use this one:

public static List<T> Rotate<T>(this List<T> list, int offset)
{
    return list.Skip(offset).Concat(list.Take(offset)).ToList();
}