Answer
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.