cjmcguinness,
I think that your square button would look better with two drop shadows. What I mean by that is adding a lighter drop shadow on the top left. I've taken your picture and re-done it with a second drop shadow to show you what I was talking about.
I did not blur the drop shadows because, in my opinion, it made it look like a more realistic shadow. Let me know what you think of this picture/idea.
(One of the pictures is on a white background so the drop shadow would be more noticeable. Both pictures are the same, just one doesn't have a background.)