Microsoft has published an awesome PDF with the specifics of how your User Interface should implement petty much every standard control you could have in your app. You can download the PDF as well as additional templates here. The additional templates are in Adobe Photoshop format. Those templates can be opened with Expression Design. Once you open these templates, you get a very high precision pixel layout that you can reference to answer all your layout questions.
Before you starting building your application it’s a good idea to go through this document, it’s only 29 pages long, however it is easier to put the control on the page correctly the first time rather than having to go back in and rework your application. Trust me, I know from experience :).
Microsoft has also published some pretty darn good Windows User Experience Design Principles, these apply equally if not more to a Windows Phone 7 application.
Another resources is the Windows Phone 7 Design Templates out on CodePlex. These is a indows Phone 7 project that do a good job of showing specific implementations of the controls. To compile this, you will also need the Windows Phone 7 Silverlight toolkit which if you haven’t downloaded and reviewed you should. It contains some missing controls like a Date and Time picker, ToggleSwitch, Context Menu, Gesture support and a WrapPanel.