In this post Gavin Wignall discusses the out-the-box controls that are available in Expression Blend.
Silverlight ships with lots of built in controls ready for use with default skins applied. All of these controls are skinable following similar steps found here with the ‘Button’ control.
To access the full list of controls available to you in Blend access the last icon in the main tool bar called ‘Assets‘. This will open up a list of available assets of which one group is labled ‘Controls‘, open up this drop down to see the full list of available controls.