Really? Colin's method seems pretty simple to memorize and work with. Especially since it's all addition mod 7. Given that the mod operator distributes over addition you can work answers out easily while working with small numbers.

For example, what day of week was September 2, 1945?

    45/4 = 11 (mod 7 = 4)
    45 mod 7 = 3 (easy to work out from 7 times table)
    September = 6
    2

So you've got 4 + 3 (disappears under mod 7) and 6 + 2 mod 7 = 1. So, the second world war ended on a Sunday.