I feel like this is something that should already exist in System.Linq

GroupingExtensions.cs

using System;
using System.Collections.Generic;

public static class GroupingExtensions
{
    public static IEnumerable<IEnumerable<T>> BreakIntoGroups<T>(this IEnumerable<T> sequence, int groupSize)
    {
        if (sequence == null)
        {
            throw new ArgumentNullException("sequence");
        }

        if (groupSize <= 0)
        {
            throw new ArgumentOutOfRangeException("groupSize", groupSize, "Groups must be of size 1 or greater");
        }

        IEnumerator<T> enumerator = sequence.GetEnumerator();

        while (enumerator.MoveNext())
        {
            yield return GetNextGroup(enumerator, groupSize);
        }
    }

    private static IEnumerable<T> GetNextGroup<T>(this IEnumerator<T> enumerator, int groupSize)
    {
        int remainingElements = groupSize;

        do
        {
            yield return enumerator.Current;
            remainingElements -= 1;
        } while (remainingElements > 0 && enumerator.MoveNext());
    }
}