Sunrise and Outlook for iPhone
The iPhone is my primary device for just about everything. With the exception of writing, design and some of the other creative projects - I use my iPhone most of the time.
Lately, I've been disappointed with Mailbox. It started off as a great tool, but has bee painfully unreliable lately.
On the other hand, I've been trying Sunrise and Microsoft Outlook on the iPhone. The combination - even for Google Apps is extremely powerful.
Microsoft hasn't been winning the mobile race, but their apps are certainly making me reconsider their stance and their direction.
Looking forward to what Microsoft produces in the future.