I originally wrote a post like this on the company blog, but since then a few things have changed so I thought I would create an updated version. The times are a bit off - my day is much more sporadic.
9:00am - Gmail
For me there really is no other choice. Being able to access email anywhere and on multiple devices is essential. Gmail powers my personal and work email addresses. And best of all - its free. That being said, I would more than happily pay for it.