There are whole bunch of tools for WPF, and more and more are popping up as WPF grows in popularity. I have listed a few of the most useful ones below, but it really depends on what you are wanting to achieve.
For instance, for me the Sketchflow plugin in Blend has made such a difference. Also, with VS2010 comming to release next year you will see the integration of VS2010 with WPF being a lot more fluid.
WPF/XAML Specific Utilities
- Microsoft Blend with Sketchflow – Design & Prototype
- Performance Profiling Tools for WPF
- XAMLPadX – Xaml editor
- XAML Power Tools – Plugin for Vs
- Snoop – Simplify Visual Debugging
- Shazzam – Edit Pixel Shading
- Mole – Visualizer With Property Editing
- Kaxaml – Lightweight XAML Editor
- Pistachio – Resource Visualizer
- Zam 3D – 3D XAML Tool
- XAML Exporter for Blender
- Paste2XAML – Convert Clipboard and metafiles into xaml
- Silverlight PAD – Test XAML Content
- StyleSnooper – See the styles for any WPF framework control
- Show me the Template – Exploring Templates of Controls
- WPF XBAP Permission Repair Tool – Repairs Registry for WPF Xaml Browser Apps
- Crack.Net – Similar to Mole or Snoop
I also agree with Andrew, if you are looking at doing a lot of WPF development it is worth giving the MVVM pattern a look at as I feel this is one pattern that does expose a lot of power behind WPF.
Also, if you havent had a look at PRISM, give it some time.